Fifty years on, Alford -- now a 69-year-old grandmother and retired New York City church administrator -- writes that she lost her virginity to Kennedy that day.
"Slowly, he unbuttoned the top of my shirtdress and touched my breasts," Alford -- at the time Mimi Beardsley -- wrote in the excerpt.
"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."
"After he finished, he hitched up his pants and smiled at me" before pointing her in the direction of the bathroom, the Post reported.
"I was in shock," Alford 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."
The young woman, described by one Kennedy biographer as a "tall, slender, beautiful" college sophomore, continued the relationship for a year and a half -- even traveling with the president on occasion -- until their affair ended with Kennedy's assassination.
Kennedy is said to have carried on numerous White House affairs during his presidency, including with an alleged dalliance with Hollywood starlet Marilyn Monroe.