Her decades-old secret about her trysts with John F Kennedy was still safe then. Outed in a 2003 biography and a New York newspaper account, Alford has learned to tell her story and not be ashamed of it from the moment she said Kennedy seduced her on her fourth day working at the White House until the affair ended shortly before his death.

In "Once Upon a Secret: My Affair with President John F Kennedy and its Aftermath," published last week by Random House, she writes of her first encounter as a naive teenager, her "varied and fun" sex life with Kennedy, whom she always called Mr President.

She was 19 and had no sexual experience when she first went to bed with Kennedy in his wife, Jacqueline's bedroom. It was June 1962.

"Short of screaming," she writes, "I doubt I could have done anything to thwart his intentions."

Nor did she want to thwart his intentions.

"I wouldn't describe what happened that night as making love," she writes. "But I wouldn't call it non consensual, either." Addressing people who have questioned the encounter, she said, "I don't consider it was rape. I have never considered it rape because I was willing."

The relationship continued, even after Alford had become engaged while attending college in suburban Boston, until Kennedy's 1963 assassination, she wrote.

The two raced rubber ducks in the bathtub; they had multiple sexual encounters, though he never kissed her; when he called her at her college dorm, he would use the code name Michael Carter, she wrote.

Her account seems "quite credible," said Robert Dallek, whose Kennedy biography made a passing reference to a college sophomore who was a favourite of the president's.

"This is how he operated," Dallek said. "He was a compulsive womaniser."

A lawyer for the Kennedy family did not respond to requests for comment over the weekend.