Exner's account cannot be dismissed. It is specific in dates and details and supported by travel documents, by her annotated appointment book, and by official logs recording three of her visits to the White House. A credible source has said Exner told him the gist of her story soon after the events in question. Giancana's half-brother Chuck has also claimed to know of contacts between the mafioso and Kennedy, and of the go-between role played by Exner.

Meanwhile, a source far more likely to be believed has stated that Robert Kennedy, supervising anti-Castro operations for his brother, ordered the CIA to assign a case officer to meet with Mafia figures. Sam Halpern, a former senior Agency official on the Cuba desk, said Kennedy himself supplied the Mafia contacts.

If such allegations - and especially Judith Exner's claims - are true, then President Kennedy was playing a horrendously dangerous game. For, throughout the presidency, his brother was vigorously pursuing his investigation of the Mafia - not least of Giancana himself. Giancana and other top mobsters evidently hoped for leniency under a Kennedy administration, as a quid pro quo for their support during the election that brought Kennedy to power. But Giancana would be overheard on an FBI wiretap saying, "The President will get what he wants out of you... but you won't get anything out of him."

If top Mafia bosses now felt double-crossed, their law - the law of the mob - might demand vengeance.

Judith Campbell Exner, who claimed she was once a mistress of John F. Kennedy and that she carried messages between the president and Mafia boss Sam Giancana, died of breast cancer September 24 in Duarte, California. She was 65 and had suffered from the illness since 1978.

Exner made waves in 1977 with her autobiography, "My Story," that included a description of her alleged affair with Kennedy.

In a 1996 issue of Vanity Fair, Exner said she ended a two-year affair because she hated being "the other woman." She also claimed she aborted Kennedy's child 10 months before he was assassinated.

She also claimed that during Kennedy's presidency she was Giancana's lover and carried messages between the president and the Chicago mob boss, including details of a plot to assassinate Cuban leader Fidel Castro.

In a 1975 appearance before the U.S. Senate intelligence committee, Exner said she had an 18-month affair with Kennedy before and after he entered the White House, and that she later had an affair with Giancana.

Before Monica Lewinsky, the was Judith Campbell Exner. Nearly 25 years ago, with the myth of Camelot still nearly intact, Exner stepped forward to reveal the first account of an affair that would tarnish the image of President John F. Kennedy. At her death from cancer on Sept. 24 in Duarte Calif., Exner, 65, was still energetically defending her story.

It was one she first told in 1975, when Senate investigators began probing reports, never proved, that Kennedy had enlisted Chicago Mod boss Sam Giancana in a plot to kill Cuban leader Fidel Castro. Exner told investigators that, as a young party girl from Los Angeles, she had been introduced to Kennedy in Las Vegas in 1960 by mutual friend Frank Sinatra. Within a matter of weeks, she said, she was in bed with JFK at New York City's Plaza Hotel, beginning a 2 1/2 year affair. "When you talked to Jack, he talked just to you." Exner told People in 1988.

Reports of the liaison, leaked to the press in 1975, stirred enormous controversy. Kennedy loyalists accused Exner of making it all up. Yet evidence showed that Exner had visited the President on several occasions in the White House and had spoken to him some 70 times by phone. "I was crucified because I had had the audacity to have an affair with Jack Kennedy," said Exner.

In 1988, Exner - recently separated from golf pro Dan Exner, whom she had married in 1975 - told writer Kitty Kelley for a story in People that, while JFK's lover, she had served as a courier between the President and Giancana. According to Exner, JFK wanted the mobster's help in nailing down votes in the 1960 West Virginia primary, and she had arranged face-to-face meetings between the two. That story drew fresh skepticism from historians, who questioned whether a candidate would be likely to have risked meeting directly with a Mob kingpin.

Her affair with Kennedy, Exner said, ended partly because she got tired of being the other woman. "I was very lonely a lot of the time," she explained. She said that she became involved with Giancana after her split with the President. Three years ago, Exner added to her story, maintaining that she had become pregnant by Kennedy and had an abortion.

Diagnosed with breast cancer in 1978, she survived more than two decades in a quiet neighborhood of Newport Beach, Calif., taking care of her cats and painting landscapes and portraits. Recently, Exner sounded more philosophical than bitter about her sensational misadventures. "I will be held accountable for my actions, which were I fell in love with a married man, and that was not proper," she told People. "But your heart rules your head in most instances, and it did with me at the time."

Judith Campbell Exner, who has died of cancer, aged 65, in a Los Angeles hospital, became notorious in the middle 1970s when she claimed that she had had an affair with President John F Kennedy from 1960 until 1962. She said she and Kennedy made love in New York hotels, at Kennedy's home and even in the White House. After her affair with the president ended, she had a brief relationship with Sam Giancana, the capo of the Chicago Mafia.

In her 1977 memoirs, My Story, she described how she arranged a meeting between Kennedy when he was running for the presidency and Giancana in April 1960, as a result of which the mobster sent an aide, Paul "Skinny" D'Amato, to West Virginia to buy support for Kennedy in the Democratic Party primary election there. She also hinted that Giancana had helped Kennedy carry Illinois, which he won by a few thousand votes in the Chicago area.

For many years, rumours circulated that Judith Campbell had also been involved in a plot hatched between her two lovers, Kennedy and Giancana, to kill the Cuban leader, Fidel Castro. In 1991 she came forward and described how she had sat on the edge of the bathtub in a Chicago hotel while the president and the Mafia don talked in the bedroom.

In April, with Jackie Kennedy away in Florida, Campbell was seeing Kennedy at his house on N Street in Georgetown, the upmarket Washington DC suburb. One night Kennedy asked Campbell to put him in touch with Sam Giancana, and within the week JFK was meeting the mafioso at the Fontainebleau Hotel in Miami Beach to arrange mob help with his Democratic primary campaign in West Virginia. After the break-up of her affairs with Kennedy and Giancana, Campbell was afraid for her life and kept her archives under the bed at her house in Newport Beach, California, guarded by a large dog, with a pistol under her pillow.

Kennedy's involvement with the Mob in a plot to kill the Cuban president has often been put forward as one of the reasons for his own assassination in Dallas in November 1963.