The young mistress of iconic US President John F Kennedy has penned a memoir detailing how he "abused and confided in her" during their affair, which ended only with his assassination.

Mimi Alford says she was a 19-year-old virgin just a few days into an internship at the White House when Kennedy seduced her in his wife’s bedroom following a pool party with two close aides and other young women.

“I was in shock,” she wrote. “He, on the other hand, was matter-of-fact, and acted as if what had just occurred was the most natural thing in the world.”

They kept up the affair after she left Washington to go to college, and she last slept with him just three days before his fatal trip to Dallas when he told her: “I wish you could come with me to Texas. I’ll call you when I get back.”

The now 69-year-old retired church administrator, who lives in New York City, uses the memoir, called Once Upon a Secret: My Affair with President John F. Kennedy and Its Aftermath, to set out in sometimes graphic detail how she spent days and occasionally nights with the notoriously sex-addicted president.

She tells how he refused to kiss her on the lips, and once instructed her to perform a sex act on one of his friends, which she did. On another occasion, he asked her to similarly “look after” his younger brother Teddy, but she refused.

Mrs Alford claimed that despite this, theirs was a close relationship, and that Kennedy often confided in her and even asked her to console him following the death of his baby son, Patrick, according to the memoir obtained by the New York Post.

At the height of the 1962 Cuban missile crisis, as the world teetered on the brink of a nuclear war between the United States and the Soviets, Kennedy hinted to his lover that he would be prepared to blink first: “I’d rather my children were red than dead.”