Fifty years after she says she lost her virginity to the president, Mimi Alford is coming forward to detail her 18-month affair with John F. Kennedy.

Alford, now a 69-year-old grandmother, says in a book that Kennedy seduced her in the first lady's bedroom when she was a 19-year-old intern, in the summer of 1962. She leaves few details untouched.

"Slowly, he unbuttoned the top of my shirtdress and touched my breasts," Alford writes, according to excerpts published by the New York Post. "Then he reached up between my legs and started to pull off my underwear. I finished unbuttoning my shirtdress and let it fall off my shoulders."

"Haven't you done this before?" Kennedy asked, Alford says. She replied, "No."

The affair isn't the only salacious story in Alford's book. She writes that at a party hosted by Bing Crosby, Kennedy popped under her nose a drug capsule said to enhance sex, and that she "ran crying from the room" because she was scared.

Another passage claims that Kennedy asked Alford to give oral sex to his friend, Dave Powers, while they swam in the pool where the intern and the president first met. She writes: "The president swam over and whispered in my ear. 'Mr. Powers looks a little tense,' he said. 'Would you take care of it?' It was a dare, but I knew exactly what he meant. This was a challenge to give Dave Powers oral sex. I don't think the president thought I'd do it, but I'm ashamed to say that I did. … The president silently watched."

And in a room with Ted Kennedy at a Boston fundraiser, the president is said to have said to Alford, "Mimi, why don't you take care of my baby brother? He could stand a little relaxation."

"You've got to be kidding me," Alford says she replied. "Absolutely not, Mr. President."

The Kennedy presidential library didn't respond to a request to answer the claims made in the book. Doug Wead, a presidential historian, said that while there's some reason to be skeptical of Alford's story, "I would tend to lean toward accepting it until it's proven otherwise."

The book, "Once Upon a Secret: My Affair with President John F. Kennedy and Its Aftermath," is also a reminder of how the culture of the White House has changed. Kennedy's private life wasn't private among those who worked in the administration and even with the press corps, but reporters shied away from sharing details.

When Alford was 60, the New York Daily News quoted her admitting to the whole affair. "All of these things are true," she said of the tabloid rumors that had floated around for years. "Remember, I was 19 years old. It was my first job."

Alford told NBC that she had "a little bit of second thoughts" when the affair began, when Kennedy swam up to her in the pool and then took her to his wife's room, but not enough to turn away.

"I should have felt guilty," she said in the interview to promote her book. "He was married to Mrs. Kennedy, but I didn't, at the time, feel guilty. I'm not going to say he loved me but I think he did like me a lot. He cared about me."

Their affair continued after Alford's internship ended and she returned to college. Kennedy would call her pretending to be a man named Michael Carter, she said, and he arranged for her to be flown to Washington to have sex with him.

The book's publisher, Random House, describes Alford as "naïve, innocent, emotionally unprepared for the thrill that came when the president's charisma and power were turned on her full-force."

She last saw him at a New York hotel a week before he was shot in Dallas. Alford says the assassination sent her into grief, and that her history with Kennedy was so much to bear that it ruined her marriage.

"Every White House is a fascinating story that is never known by its generation. It's only successive generations that learn all these stories," Wead said. "Without those private stories, sometimes you can't understand history."