She had already suffered the torment of losing one man she loved.
And sitting at the hospital bedside of her brother-in-law, Jackie Kennedy was about to lose another.
According to a new book, the widow of President John Kennedy had a steamy four-year affair with his brother Bobby.
The relationship was so intense that when Bobby was gunned down during his 1968 presidential campaign, it was Jackie - and not his wife Ethel - who instructed doctors to turn off his life support machine.
Ethel, mother to Bobby's 11 children, knew about his affair but chose to ignore it, according to the book, Bobby and Jackie: A Love Story, by C.David Heymann, who has written extensively about the Kennedy clan.
A host of political insiders and celebrities are quoted in the book, which will be published in the U.S. next week. 'Everybody knew about the affair. The two of them carried on like a pair of lovesick teenagers,' the late Franklin Roosevelt Jr., who served in John Kennedy's White House, is quoted as saying in the book.
'I suspect Bobby would've liked to dump Ethel and marry Jackie, but, of course, that wasn't possible.'
Heymann, who claims to have trawled through FBI and secret service records as well as talking to Kennedy family and friends, says Bobby was the former First Lady's one 'true love'.
He says their romance grew from their shared grief over the assassination of John Kennedy in 1963.
'It was the coming together of a man and a woman as a result of his bereavement and her mental suffering at the hands of her late lecherous husband,' Jackie's confidant, writer Truman Capote is quoted as saying in the book.
'It was passionate but it was doomed,' he added.
Jackie flew to Bobby's hospital bedside after he was shot by Sirhan Sirhan following his presidential primary victory in California on June 4, 1968.
Heymann writes that Ethel allowed her love rival time alone with her dying husband.
Although Bobby was brain dead, Ethel refused to pull the plug and his brother Teddy was too distraught to decide.
So it was left to Jackie to order the respirator to be turned off and sign the consent forms, the book claims.
Kennedy historians say Heymann, who also claims Jackie had an affair with Marlon Brando, exaggerates the relationship between her and Bobby.
But his book includes telling recollections from a variety of family friends, some of which were published yesterday in excerpts in the New York Post.
They include a close encounter on the presidential yacht in May 1964, just six months after JFK's death. Bobby and Jackie are said to have 'exchanged poignant glances' before disappearing below deck, leaving Ethel upstairs.
'When they returned, they looked as chummy and relaxed as a pair of Cheshire cats,' Kennedy friend Arthur Schlessinger says.
By mid-1967, Jackie was contemplating marrying Greek shipping tycoon Aristotle Onassis, but agreed to wait until after Kennedy's 1968 presidential run.
Bobby apparently told former JFK press secretary Pierre Salinger: 'She'll marry that man over my dead body.'
Jackie became Mrs Onassis four months after Bobby's death.