The author - now 72 - has admitted that she dated the Hollywood icon briefly in 1954 after meeting him at a showbiz party with her older sister Joan Collins, just days after she was expelled from school.
She said: "Marlon was in his early 30s and I was about to be 16. He sent someone over to me to say, 'Marlon thinks you're great looking and have a great body and would like to meet you.'
"We had a very brief but fabulous affair. He was at the height of his fame and gorgeous."
Jackie has previously spoken of her romance with the actor - who died in 2004 aged 80 - but never revealed how old she was when it happened.
She admitted in 1995: "He started straight at my 39in chest - men often talk to my chest - and said, 'That's a great looking body you have, little girl.' It was a mutual attraction.
"It was such a thrill for me because it was the most amazing introduction to Hollywood. I had only been there a week.
"I saw him on and off for a while and then it was over. He was a great character."
Had Jackie revealed the affair at the time, the 'Godfather' star could have faced up to four years in prison as under Californian law, it is illegal to have sex with anyone under the age of 18.