It was at a dinner party in Georgetown, Washington DC on May 8, 1952 that Jackie and Jack connected. Kennedy was just over two weeks short of his 35th birthday and already a public figure. After five years as Massachusetts representative in Congress, he was running for senator. Recently he had been voted "America's Most Eligible Bachelor".

Tall, skinny, with a shock of brown hair, Jack Kennedy's attraction came from his personality as much as his looks. Women – and men – fell over themselves to please him. Inga Arvad, his lover from November 1941 until his father broke up the relationship in February 1942, had written of him at their first encounter: "He had the charm that makes birds come out of their trees."

Jack Kennedy and Jacqueline Lee Bouvier had many things in common. Like Jackie, Jack was immensely well-read. Unlike the rest of his family, who had no intellectual or literary pretensions, he had been an avid reader from his childhood when he spent hours alone through continual bouts of sickness. At three he nearly died of scarlet fever, and he was constantly ill during his schooldays. In 1934 he was so ill that prayers were said for him in chapel. In 1947 Addison's disease had been diagnosed.

A deficiency of the adrenal glands, Addison's disease in its more severe form can lead to physical weakness and psychiatric symptoms including irritability, nervousness, emotional instability and depression. Steroids in the form of cortisone could be deployed to counteract the deficiency and avert the symptoms. Nevertheless, the treatment itself was tricky and could produce serious side-effects. A too-low dosage leaves the patient tired and weak, but too much may lead to psychotic symptoms.

Jack might have made up his mind, as he later claimed, at that dinner in Georgetown, that Jackie was "the one", but if he had, he showed no immediate sign of it. He invited her to the Kennedy family home at Hyannis Port on Cape Cod; she briefly joined his campaign in Boston, but he continued to see other women. His courtship was sporadic and somewhat furtive; on their first date together he brought along one of his political henchmen, Dave Powers, as a chaperone.

Jackie attended Eisenhower's inaugural ball in January 1953 as Jack's date but the senator, as he now was, still showed no sign of proposing. For Jackie, the situation was not comfortable. At home, little sister Lee had beaten her in the marriage stakes by getting engaged. Lee's marriage to Michael Canfield was celebrated at Holy Trinity Cathedral in Georgetown on April 18, 1953. Within a month of catching her sister's bouquet, Jackie had succeeded in luring the senator from Massachusetts into proposing marriage.

It happened after she began translating ten French books on Southeast Asian politics as material for Jack's first major big Senate speech. She later joked that she had done this to make him marry her. No doubt her accomplishments in this field did impress him, but there were other factors weighing in her favour. Jack was approaching his 36th birthday, and he had been dating Jackie for more than a year. While he was still seeing other women, she was definitely the most suitable girl on his horizon. He was not in love with her. Being "in love" was not a state of mind he had experienced. Ten years later, shortly before his death, when asked by a friend whether he had ever been in love, he replied, "No, but I've been very interested once or twice."

Jackie certainly came into that category. He was intrigued by her, by her elusive, teasing quality, her wit and sharp judgment of people, her love of history and literature that matched his own. Physically, she was not his type; lean, dark and flat-chested, she was precisely the opposite of the curvaceous blondes he favoured. Sexually they had little in common: to Jack sex was no more than the satisfaction of a basic urge. Jackie was not frigid but she was sexually inexperienced and expected romance. Until then she had kept men at arm's length, following the accepted rule that if you wanted a good husband you had to be a virgin. Sex was not of primary importance to her; she wanted passion, which she was never going to get from Jack Kennedy.

Intrigued by Jackie's adoration of her father, Jack took the trouble to become friendly with Black Jack Bouvier. "They talked about sports, politics and women – what all red-blooded men like to talk about," Jackie recalled. "They were very much alike." One might wonder how much Jack, with his interest in history and world affairs, would have liked close comparison with a man whose interest in the world did not extend beyond casual sex and dedicated gambling, but he was amused by the old rogue and Black Jack, although convinced that no man could be good enough for his daughter, was charmed in return. But in equating Jack Kennedy's "red-blooded" male behaviour with Black Jack's and thinking she could handle it, Jackie was making a serious mistake. As she was to find out, there was less in common between the two men than she fondly imagined: on the scale of womanising, Jack was ten to Black Jack's two or three.

Weighing heavily in Jackie's favour as a bride for Jack was the active support of his father, Joseph P Kennedy, the man who "made it all happen". In Joe Kennedy's view, a senator required a wife. Couples married young in the Fifties, and a man who reached Jack's age but was still a bachelor risked being branded a "faggot". Jackie had all the qualifications to be Jack's wife, the type of wife a rising politician needed as an accessory to his career. She was beautiful, intelligent and strong-minded enough to cope with him in so far as any woman could. She was a Catholic with an entrée into the WASP world.

Joe Kennedy was well-informed enough to know that the Bouviers as a family were washed-up and that Black Jack was a financial failure with a reputation as a drunk. But Jackie herself was the perfect package for his son and he was prepared to buy her.

So Jack proposed one evening in early May. Jackie played hard to get but she knew that this was a decision she could not take lightly. On May 22 she left for England on a trip that would be a perfect opportunity to consider whether, after all, now that she had achieved her objective, she really wanted to marry him.

Friends warned her that Jack was an inveterate womaniser. But this flaw was balanced by the fact that he had money. Attracted to him as she undoubtedly was, Jackie would never have married a poor Jack Kennedy. Even Jackie's closest admirers could see her obsessive pursuit of money as a fault line in her character. "She had a primeval fear of poverty," said a man who knew her in her Onassis days. "She had an insecurity about money, a fear of going back to being poor."

Her sister, Lee, thought that, for Jackie, money was "insulation. She'd seen enough downfall round her to want that insulation." John White put it more unkindly, "All she was fundamentally interested in was money. That was really the guiding motive of her life." Jackie's experience of the hard realities of life so far, the decline of the Bouvier fortunes and the transformation in her mother's position as a result of her marriage to Hughie Auchincloss, had impressed on her that marriage to a rich man, preferably a very rich man, was the only true security.

When the plane on which Jackie returned home touched down in Boston en route for Washington, Jack Kennedy was waiting for her. The die was cast. The wheels had been turning inexorably since the official announcement of the engagement on June 24, 1953. In true Kennedy style, Joe went to great lengths to extract the maximum publicity out of the celebration of his son's marriage. The local press devoted the front page and many columns to what it described as "Newport's most brilliant wedding in many years". Special traffic arrangements had to be made; the crowds gathered outside the church to gawp at the celebrities invited by the Kennedys, who were almost outnumbered by movie and press cameramen. The ceremony was conducted by the Kennedy's friend, Archbishop Cushing of Boston, who read out a special blessing from Pope Pius XII before the nuptial mass.

Jackie was serene. Jack and his bride posed without stint for the photographers, Jackie balking only once when she was asked to pose with her husband clinking champagne glasses, pronouncing it "too corny". Just as the irresistible tide of Kennedys and their friends had swamped her Newport wedding, Jackie found herself swept irrevocably into a Kennedy future.

Jackie came to understand that Jack's most significant attachments were to men, not women; he preferred the company of men. He was a natural leader, a pole of attraction, and had been since he was a skinny schoolboy at Choate. Schoolmates, college friends, Navy buddies, English aristocrats, political operatives, men of the Secret Service detail guarding him when he was in the White House, all were devoted to him. His male friends gave him their absolute loyalty, and his loyalty to them was equally unswerving.

But where women were concerned, Jack Kennedy had inherited his father's genes and absorbed his father's attitudes. The Kennedy approach to women was profoundly misogynist. This was partly the Irish tradition regarding women as divided into two distinct groups, for procreational or for recreational purposes, with wives definitely in the former category. This stereotype was reinforced by the acquiescing attitudes of Kennedy women like Rose, and Bobby's wife Ethel, who saw sex primarily in reproductive terms, Rose's nine children being surpassed by Ethel's 11. More importantly, it was the result of Joe's particularly crude view of women, whom he considered as no more than sex objects to be conquered, with no other purpose or interest beyond his immediate sexual gratification.

Joe's predatory behaviour went far beyond what would normally be considered acceptable: no attractive female was out of bounds as far as he was concerned, and that included his sons' girlfriends. When these girls were staying at Hyannis Port or Palm Beach, he would try to persuade them to sleep with him. Worse, there was competition between Jack and his father over women: each got a thrill from sleeping where they knew the other had gone before.

As Inga Arvad's son recalled of "the Ambassador's" attempts to seduce her the moment Jack left the room, "It was a totally amoral situation. There was something incestuous about the whole family. Joe set the pattern for Jack by importing tarts to Hyannis Port and Palm Beach when Rose was not there. On one occasion Jack returned home from school to find his bed covered with sex magazines, "all open to show the female anatomy at its most immodest", left there by his father."

Joe showed no loyalty to any of his women; not even to Gloria Swanson. According to one source, he boasted to Jack and Jackie about sleeping with Swanson, and gave coarse details about her genitalia.

Jack was sexually more successful than his father as he was infinitely more attractive. Women of every age and class fell for him, while Joe went for easier game — showgirls, secretaries or call-girls. But Jack was more sexually driven, to the point of satyriasis. Some people have attributed his promiscuity to lack of maternal affection, others to his brushes with mortality, which left him with a desperate need to take all the pleasure he could before death overtook him. Certainly it increased as he grew older until it reached addiction, the full extent of which Jackie never grasped.

Jackie, however, was tough enough not to be cowed by the Kennedys. Despite her slimness, she was physically as strong and athletic as they were, with her muscular, slightly bowed legs and large hands. Jackie's method of dealing with the Kennedy tribe was quietly to assert her independence. She stayed out of the relentless activities – tennis, sailing, touch football – but not because she was too delicate for them. William Manchester remembered her "playing touch football like a gazelle".

Intellectually she could beat them at one of their favourite games, a form of charades called "The Game" in which opposing teams had to act out a given phrase or word for their team-mates to guess in a race against time. For the Kennedy women, however, the bitterest pill they had to take where Jackie was concerned was that she had so swiftly conquered the heights of the Kennedy pyramid – the two most important males, Joe Kennedy and Jack.

Jackie loved her father-in-law. After all, she had been brought up to cope with dominant males and she used all her skill to win over the Kennedy patriarch. With the women she did not even try.

Jackie was romantically in love with her husband, but romance was hard to sustain in the circumstances of their early married life. Among the disappointments was Jackie's failure to follow the pattern expected of a Kennedy wife and bear a child in the first year of marriage. Whether the difficulties she was to suffer both in getting pregnant and in bearing healthy children to full term were on her side or due to her husband's health problems is a moot point.

While still at Harvard in 1940 Jack had contracted venereal disease, described by his doctor at the time as a mild, non-specific urethritis. Ten years later, in 1950, he was reported as suffering a "slight burning on urination", the result of "a mild, non-specific prostatis", which was treated with various antibiotics, painful prostatic massage and sitz baths. Through the winter of 1951-52, Jack had suffered "recurrent symptoms" and in March 1953 he was referred to Dr William P Herbst, a Washington urologist. According to Herbst's almost illegible notes, Jack complained of "burning in prostate area" and made four subsequent appointments for treatment.

Jackie succeeded in conceiving in the first year of their marriage but miscarried. The underlying cause of this and her subsequent history of childbearing — a stillbirth and two premature births — was almost certainly chlamydia, contracted from Jack as a result of gonorrhoea that he contracted while still at Harvard in 1940. Non-specific urethritis, which was diagnosed in him in 1950, is now known to be a result of a chlamydial infection.

It is unlikely that Jack confessed his medical problems in this respect to Jackie, first, because he hated discussing his various ailments, however serious, and second, although in fairness she should have been the first to be told, he would almost certainly have preferred her to be the last.

As the wife of the Kennedy crown prince, Jackie could not help feeling humiliated by the abounding fertility of the other Kennedy wives. For her, it was a hidden tragedy: if she had succeeded in bearing a child that first year, or even the next, it would have saved her from some of the heartbreak and marital difficulty she experienced over the next few years.

Jack had hated giving up his bachelor status and his freedom and had done so for a complex series of reasons, of which "having a family" was one. As a rich young bachelor his needs had been catered for by a loyal band of retainers; he had the company of his family and many friends, and as many women as he wanted when he wanted. At 36, it was difficult to change his attitudes to accommodate an insecure young wife. He began to feel trapped.

Jackie worked hard to make her marriage a success. But politics and politicians remained for her a largely uncharted area into which she had no desire to venture. To the Kennedy women politics and public life were as natural as the air that they breathed, and Jack had taken it for granted that Jackie would be the same. He was disconcerted to find that she was not. It was a quality in her that he came later to appreciate, but in the early years, it contributed to mutual misunderstanding.

Less than six months after his marriage, Jack was hankering for his old life. He had not forgotten a beautiful blonde Swedish girl he had met in the South of France on his pre-wedding jaunt the previous August. On March 2, 1954 he wrote to Gunilla von Post telling her that he planned to return to the South of France that September, and followed it up with a series of telephone calls to Stockholm.

Jack's letters to Gunilla were based on a desperate optimism: he was trying to hold on to a dream of youthful romance and pleasure when the reality was a daily agony and the prospect of serious invalidism. He had been born with one leg shorter than the other, a condition that would have caused problems even if he had not injured his back playing football at Harvard or ruptured a spinal disc in the Second World War. In the spring of 1954 his secretary, Evelyn Lincoln, began to notice that he was having increasing problems with his back. If he dropped something, he had to ask her to pick it up for him. He was using crutches to walk, but hid them from official visitors.

"Soon his efforts to disguise the agony he suffered, together with his demanding schedule, became a heavy drain on his nervous energy," Lincoln wrote. "He became increasingly irritable ... "

By August, Jack's spinal deterioration had worsened to the extent that drastic surgery was necessary to save him from life in a wheelchair. The danger of the operation, known as a lumbar fusion, was infinitely increased by the Addison's disease, which lowered his immunity to infection. On October 11 he was admitted to hospital and on October 21 the operation was performed by a team of four physicians. Jack survived, but within days, as he had been warned, infection set in. He slipped into a coma; twice his family was summoned to the hospital and the last rites were performed as he approached death for the third time in his relatively short life. Against all the odds he fought back.

While Jackie's care for Jack was unquestioned, she was angry when Grace Kelly visited him in hospital. One of the most beautiful film stars of the century, most men were in love with, and most women copied, Kelly's cool blonde high-society looks. In real life she was not only beautiful but warm and funny. Jack had never made any secret of his admiration for her. Gore Vidal recounts a vignette of Jack and Jackie looking at press coverage of Grace's wedding to Prince Rainier in the summer of 1956 when apparently Jack said, frowning, "I could have married her!", and dates Jackie's well-documented dislike of Grace from then. According to Robin Biddle Duke, it was Grace's visit to Jack in hospital that first raised Jackie's hackles: "Grace Kelly then became somebody in Jackie's life that she could not abide."

If Jackie was jealous, she was too clever to show it. But she took against certain women in his past who remained his friends, and close to him long after anything sexual between them was over. With Jackie, feelings ran deep. Jack could not understand her moods, her withdrawal and prolonged sulking when she was upset. He complained about her: that she was cold, a prima donna, a spendthrift and often about her voice. And yet he was fascinated by her and tried to placate her, even to the extent of forbidding an old friend to come to his wedding because of Jackie's feelings about her.

The operation had not been a success, and in February 1955, suffering from a near-fatal infection, Jack was back in hospital to have another operation to remove a metal plate that had been implanted in his back. Once again his life was at risk and once again he recovered. Back in Palm Beach, Jackie's devotion to amusing and even nursing him impressed everyone. But Jack's physical discomfort made him difficult with Jackie. Betty and Chuck Spalding visited to cheer him up. "We were all down in Palm Beach and they had some sort of spat. Jackie just went off to the other side of the pool, to a little place, went off by herself. Jack was just difficult to get on with. It was very difficult for both of them really, because Jack just had a fear of intimacy and I guess Jackie did too." Both of them seemed to have some sort of emotional block towards each other.

By the summer of 1955 Jack and Jackie needed time away from each other. Jackie's arrival in England alone to stay with her sister Lee in the first week of July sparked rumours that the marriage was in trouble. Jackie took refuge with her sister Lee and brother-in-law Michael Canfield at their chic but tiny apartment in Belgravia. Lee and Michael were a popular and glamorous couple on the English social scene. They were based in London where Michael had a pleasant sinecure of a job, wangled by Lee, as special assistant to the American ambassador. Jackie and Lee were particularly close at that time of their lives. Both their marriages were in trouble; both were intent on enjoying themselves to the hilt. Social weekends in the country and endless parties in London restored Jackie's battered morale.

Meanwhile, Jack had a renewed rendezvous with Gunilla von Post. He was travelling with Torby MacDonald, now a congressman, a boon companion in Jack's sexual adventures. They arrived in Sweden on August 11, Jack still on crutches, for a week's successful romance with Gunilla. Although Jack never spoke of his wife, Torby did, "slipping some clues about Jack's unhappy marriage" to Gunilla and telling her that Jackie "was not that concerned" about Jack. If Gunilla is to be believed, Jack had in mind the idea of leaving Jackie and marrying her. Joe Kennedy stood in the way: father and son had an irascible telephone conversation, after which Jack reported: "He doesn't even want to hear about my troubles with my wife — because she likes him, and he responds to that."

As well as Joe Kennedy, Jack's ambition stood between Jackie and divorce. The romance with Gunilla and talk of divorce from Jackie were his last attempts to break free of his destiny. That autumn of 1956 rumour had it that Jackie had been offered a million dollars by Joe Kennedy to stay with Jack, which, as Jackie joked, was hardly a huge bribe — "Why not ten million?" she asked Joe, when the story came out in Time. There was no doubt, however, that she had talks with Joe, whom she knew to be overwhelmingly on her side. In realistic terms, the stronger the Kennedy ambitions for the Presidency became, the more the strength of her hand increased. At Thanksgiving 1956, while Jackie was in Europe, Jack and Joe held a conference at Hyannis Port, during which they agreed that Jack would run for the presidency in 1960.

As long as Jack confined his extramarital activity to the campaign trail, and to a room at the Mayflower Hotel when he was in Washington, his philandering affected Jackie less than did his lack of consideration for her and her relegation to second-class female status within the Kennedy clan. She could accept the infidelity, à la Black Jack: it was standard behaviour in the international circles in which she now moved. What she found difficult to deal with was that, in his eyes, she was not number one, a position she had been accustomed to occupy practically since birth with the men of her family and circle of friends.

She was soon to lose the man with whom she had always been number one. Neither Jackie nor Lee was aware that Black Jack was seriously ill, or that he had cancer of the liver when he checked into Lenox Hill Hospital in July 1957 for a series of tests that apparently revealed nothing. Jackie, who had been spending the summer at Hyannis Port, flew up to see him but, thinking there was nothing seriously wrong with him, spent her birthday with her mother at Hammersmith. On 3 August he lapsed into a coma and died, riddled, apparently, with galloping cancer. Jackie, this time accompanied by Jack, arrived just too late to say goodbye.

For Jackie, Black Jack's death was the worst emotional shock of her life so far. It signalled the passing of an era while the birth, four months later, of her daughter opened a new phase in the Kennedy marriage. She delivered the longed-for baby on November 27, 1957. She named her daughter Caroline Bouvier after Lee and Black Jack. The first time Jackie saw her daughter was when Jack wheeled her in. He had been sitting in the waiting room to wait for the birth. A friend who was with him at the hospital recalls Jack's face when the doctor came into the room and told him that the baby had arrived. "I will always remember the sweet expression on his face and sort of a smile."

As plans for the presidential campaign of 1960 gathered pace, Jackie had felt extreme misgivings about its effect on their lives. She wondered whether it was really worth it to have Jack run for the presidency when she never saw him and Caroline together in the same place two days running, and when she did see him they were usually too tired to speak to each other. Intensely private as she was, Jackie was deeply concerned about the demands that public life would make on her and her family. The future held other fears. In conversation with Walter Reuther, president of the United Auto Workers, Jackie expressed her concerns about the presidency in general and assassination in particular. (Gunmen had attempted to kill Walter Reuther in 1948 and his brother Victor Reuther in 1949.)

"She really was obsessed," Reuther's companion, Jack Conway recalled, "with this whole idea of the change in her life, the change in Kennedy's life, and how do you protect against assassinations. She wondered what security precautions did to family life."

There were problems when Jackie's "sense of good taste" clashed with the Kennedy family's wishes. There was an acute difference of opinion between them over the Sinatra Rat Pack. Jackie did not like the Rat Pack trio of Frank Sinatra, Dean Martin and Peter Lawford for whom the Kennedy family had an almost star-struck regard. She was certain that the Rat Pack was the wrong image. Joan Braden recalls, "I was Jackie's liaison with campaign headquarters and I was to make her wishes known; and I dreaded what might be the confrontation. But it was done. The Rat Pack disappeared from the campaign."

Jackie had every reason to keep Sinatra away from the campaign and, even more, the candidate. Publicity had linked the singer with the Mafia since 1947. She was intelligent enough to know that the games played by Sinatra and Peter Lawford were far from innocent. No doubt she suspected that when her husband was with Sinatra he liked to play them too. One of the singer's attractions for the Kennedys was that he was a source of girls. On February 7, 1960 Jack left the campaign plane at Las Vegas, en route to Oregon, to catch a Rat Pack show at the Sands. It was on that occasion that Jack met Judith Campbell, an Elizabeth Taylor lookalike. Within a month he had embarked on a two-year affair with her, which involved him in a dangerous connection with the Mafia, for she was also a girlfriend of the Chicago mobster Sam "Mooney" Giancana. At Kennedy's request she effected an introduction to Giancana, and thereafter in April 1960 she acted as a courier between Kennedy and the Mafia leader, carrying a satchel of money for deployment in the Illinois primary.

However, the most potent weapon in the Kennedy armoury in the 1960 campaign was not the superiority of the Kennedy political machine, oiled by vast amounts of Joe Kennedy's money, but television, which Jack was the first politician to deploy with devastating effect. By 1960, 88 per cent of American families owned a set, as compared with only 11 per cent ten years before. On 26 September, the first of the four "Great Debates" on television between Kennedy and Nixon was broadcast. Nixon suffered from the televisual defect of having an unusually transparent skin so that every hair follicle showed up on camera, even if he had just shaved. He was tense, unnerved by technical complications in the studio during the day, while Kennedy was relaxed after a brief, anonymous sexual encounter shortly before the debate. Those who heard it on radio thought that the candidates had come off equal, but polls of those who had watched it indicated that Nixon had come out of it poorly or even very poorly.

On the morning of election day Jackie got up early to be driven to Boston to meet Jack and cast her vote, before returning with him to their house to begin the long wait for the result. Jack was edgy, his response to the welcoming crowd at Hyannis airport perfunctory and his smile half-hearted and strained. Shortly before six, while Jack and Jackie were asleep, Secret Service men, a sure sign of official recognition of the transfer of power, joined the police manning the cordon point outside the compound. At 9.30 Ted Sorensen arrived to confirm what the Secret Service men already knew. Jack had been elected 35th President of the United States.

Jack's women

The thought of Jack’s ‘women’ lay like a shadow across Jackie’s life, and there were times when privately she nursed agonising doubts about her ability to sustain the reality behind the family façade. In February 1958 she had opened her heart to Walter Ridder, newspaper publisher and Merrywood neighbour. ‘I don’t know if I can stay with him, he is so unfaithful.’ Walter said to her, ‘The terrible thing for you, Jackie, is, it’s not a decision you can make on a personal basis. If you should leave him and divorce him, there is no way that he can be President, and I doubt that you want that mark on your life.’

Jackie learned about the women in Jack’s past – from Jack. ‘You know, in the end, Jackie knew everything,’ William Walton said. ‘Every girl. She knew her rating. Her accomplishments … I mean, everything that was worth knowing, she knew. And she always had that kind of … she will get it out of you so you might as well give in quickly because you’re going to.’

The women whom Jackie seems to have most resented were those who were close to Jack in a way that she seemed unable to achieve. She found these close platonic friendships difficult to handle

When it came to Jack’s sexual affairs, Jackie closed her eyes to those she did not see. Apart from casual sexual encounters, Jack was regularly sleeping with at least three women in the year before he entered the White House – Judith Campbell (later Exner), an unnamed Radcliffe student, and the woman whom Jackie was to name as her press secretary, Pamela Turnure.

Jack’s relentless womanising represented an unexploded bomb under the Kennedy White House. Although at one point he had seemed to envisage the curtailment of his adventuring when he reached the Presidency – ‘I suppose my "poon" [womanising] days are over,’ he had scribbled idly, while on the campaign plane – the scale of his sexual risk-taking actually increased during his years in the White House. In the ultimate analysis, Jackie’s loyalty and strength of character, her sense of dignity of the American Presidency were Jack’s only real insurance against disaster. J. Edgar Hoover, the director of the FBI, had no fewer than six files involving Jack Kennedy’s ‘sexual misconduct’, dating back to his affair with Inga Arvad. When Kennedy was being considered as the Democratic vice-presidential nominee in 1956 Hoover had asked for a name check; on being told what was in the files, he had been ‘shocked’. ‘Hoover was a close friend of Ambassador Kennedy and … did not want to be responsible for a report that would damage the political career of old Joe’s promising son.’ But the Kennedys had every reason to placate Hoover: by 1960 his Bureau held enough explosive material on Jack to blow his Presidency out of the water.

One file raised allegations of electoral fraud by the Kennedy campaign in West Virginia, which included not only vote-buying but the relocating of voting places and even the operation of handles on voting machines by local officials in place of voters.

What should have been the happiest day of Jackie’s life so far, her wedding day, turned out to be one of the bitterest. Her father, Black Jack Bouvier had been looking forward to cutting a dash at Jackie’s wedding. He had dried out, taken time to get himself in perfect shape, jogging round the reservoir in Central Park. As the father of the bride, he had booked into the best hotel in Newport, the Viking, not far from the church of St Mary where Jackie was to be married. According to Gore Vidal, Jackie’s mother, Janet, sent Michael Canfield to the hotel to ‘tell her ex-husband that he could of course come to the church and give away the bride but he could not come to the reception’. Janet, he said, did not tell Canfield to ply Black Jack with alcohol and get him drunk, as one story had it. ‘Mike Canfield was a gentleman, something which practically none of this cast is, a real gent … Mike fulfilled his mission feeling rather guilty about it and he said that old Jack took it quite well, he thought, and he just left him there and of course Jack went straight to the bar.’

Lee remembers the episode as a searing experience: ‘I never saw my father out of it or drunk until the worst day there could have been in his whole life, at Jackie’s wedding. It was more than understandable but I think that perhaps I was the only one who knew how he felt in total enemy territory, completely on his own. Understandably he just got completely drunk the night before, unable to give his beloved daughter away the next day. Right after I went through the wedding, I chartered a little plane and took him back to New York and put him in the hospital for a while. It was particularly heartbreaking because he had been looking forward to this moment for months and sort of had himself in training for it – I suppose one of his greatest weaknesses, far more than alcohol, was that he was very vain. As he adored Jackie this was the moment, the biggest, the most important moment in his life …’ It was the cruellest thing Janet could have done to both Black Jack and Jackie, a sign of the tremendous bitterness she still felt towards him. ‘My mother …,’ Lee said, ‘… a woman’s revenge is relentless and she just felt that she would fee extremely uncomfortable if he was in the house. I don’t know why – I think it would have added to the festivities enormously and, of course, given my sister the greatest pleasure.’

Old Joe Kennedy was the King-Emperor at the apex of the Kennedy pyramid. Tall, well-built and possessed of what one of his son Jack’s aides described as ‘outrageous charm when he wanted to use it’, Joe Kennedy was a cold-hearted, brilliant, ambitious and proud man. Both in his private life and in business, hew as selfish, single-minded, ruthless and amoral.

The grandson of penniless Irish immigrants, Joe Kennedy quickly perceived that money was the source of power. By 1914 he had become the youngest bank president in Boston. He planned to found his own dynasty to rival the old Boston families, which controlled the financial and social levers in the city. When he was just under eighteen, he had picked out the sixteen-year-old Rose Fitzgerald, the favourite daughter of John ‘Honey Fitz’ Fitzgerald, one of the most popular and successful of the Boston Irish politicians, as a suitable bride.

When America entered the First World War in April 1917, Joe refused adamantly to enlist and was branded a physical coward for the first but not the last time in his life. It was a stain on his name that his two eldest sons would attempt to erase by their own extraordinary heroism. Instead, he concentrated on making money: bootlegging during Prohibition from 1919, which inevitably put him in contact with organised-crime figures, and on the stock market, learning the secrets of insider dealing and stock pooling. By the mid-1920s, with no visible source of income since he had left his brokerage firm in 1922, Fortune magazine estimated his wealth at some $15-20 million in today’s money. In 1926 he moved on to Hollywood, using the same ruthless expertise to make a great deal more money, and earning himself a reputation as a swindler and double-crosser in the process.

Money, however, and in particular the methods he had employed to get it, did not bring Joe the social recognition he craved. Rejected by the Cohasset Country Club, he moved his family to Riverdale, New York, in 1927. While Joe was convinced that his rejection by his country-club peers was prompted by pure prejudice – ‘because I was an Irish Catholic and the son of a barkeep’ – others said it was his bad financial reputation that barred him. Fear of prejudice prompted him to acquire his summer home on Cape Cod in an area he had been assured would accept him.

Having survived the 1929 stock market crash by selling short, Joe was soon enriching himself once again through predatory insider share dealings. That year, boosted by an ever-increasing fortune and connections with the new President Roosevelt, Joe bought a house on North Ocean Boulevard, Palm Beach, the winter habitat of the seriously rich. In 1934, declaring, ‘It takes a thief to catch a thief,’ Roosevelt appointed him to regulate the stock market through the Securities Exchange Commission.

Joe Kennedy’s ambitions now soared far beyond Wall Street: with his usual single-minded analytical perceptiveness he had diagnosed that, after the crash of 1929, the real seat of power had moved from Wall Street to Washington, from business to government and the highest office in the land. Having supported Roosevelt, both financially and behind the scenes in the 1932 presidential election, he expected to be rewarded with office. He was given the secret promise of the social summit that both he and Rose craved: the London embassy. In February 1938 he sailed for England, eventuallly joined by his wife and all nine children, as the United States’ first Catholic ambassador to the Court of St James.

For Rose it was perhaps the happiest time of her life. All social doors were open to the Kennedys: they were asked everywhere and even spent the weekend at Windsor Castle with King George VI and Queen Elizabeth. Just over a year later, however, when war broke out in Europe, Joe Kennedy’s energetic advocacy of appeasement of Hitler made him deeply unpopular. His craven attitude was exposed when, even before the Blitz, he rented a mansion outside London to escape possible bombing at night, leaving his embassy staff to face the danger. It reinforced his justified reputation for physical cowardice.

In October 1940, on the eve of the presidential election, he virtually blackmailed Roosevelt into recalling him and on his return gave an interview of such indiscretion that it ended his hopes of a political career. Among other things, he pronounced democracy in England ‘finished’ and declared that the Queen of England would be among the first to make peace with Hitler. Even after American entered the war in December 1941, he continued to voice isolationist views, making himself virtually a social pariah and one of the most unpopular men in America. By 1942, shunned by Roosevelt, with whom he had quarrelled, and widely detested by the American people, Kennedy realised that any hope of a future in public life was definitively over. All his hopes, ambitions, formidable energy and financial clout would be concentrated upon his children, his eldest sons in particular. As Jack’s biographer wrote, ‘In the circumstances, only his sons Joe Jr and Jack could restore the family honour.’ And after the death in action of Joe Jr in August 1944, that responsibility rested solely upon Jack.

Just as Jack would have Bobby as his trusted ally in the White House, so Jackie, isolated as First Lady and wary of trusting women, would rely upon Lee. ‘Jackie was happiest when her sister was around,’ Mary Gallagher wrote, ‘because Lee was the one person with whom she could relax and pour out her feelings.’ The White House years were the closest of their adult relationship. Jackie needed Lee and rewarded her with the highest favours at her court; in return, Lee was happy to act as lady-in-waiting and to enjoy them.

The Jackie-Lee relationship was as competitive as ever. At the time of Jackie’s engagement to Jack, friends had reported Lee as jealous that her sister had captured the handsome, rich young Senator. Lee and Jack found each other attractive and during his early troubles with Jackie, he had been heard to complain that he had ‘married the wrong sister’. Getting into bed together was bound to happen, at least once. Michael Canfield told Gore Vidal that the first time had been in the south of France and that Lee had made no effort to conceal it from him. Jackie found out, quite when nobody knows, but during the late seventies in long talks with her sister-in-law, Joan Kennedy, she confessed that she had known about it.

By 1960 Canfield was out of the picture, as far as Lee was concerned. In February 1958 she had left him for Stas Radziwill, with whom she had been having an affair. Stas was nineteen years older than Lee and in some ways, therefore – apart from his resemblance to Black Jack – represented the father-figure she sought for security. That he was rich, a prince and popular with the international set, made him a desirable prospect. Stas cherished his family in Poland, his upright, gallant father Prince Janusz, whose wife, Princess Anna, had died while both were imprisoned in a Soviet concentration camp, and who, after refusing to head a post-war puppet government, had lost all his possessions and lived in a two-bedroom Warsaw flat. Stas supported him, despite his painful awareness that his father regarded him as the black sheep of the family.

‘Where Stas was clever,’ said a friend, ‘was that he sensed that the important man was Kennedy, long before anyone else saw this.’ The Kennedys adored him. Jackie in particular loved her eccentric Polish brother-in-law and was loved by him in return. ‘He liked Jackie because I think Jackie had this feeling for him,’ a friend said. ‘I don’t mean physically but she really liked him.’