According to the book, Monroe fully believed the President was going to leave his wife and marry her, reportedly telling her friend Jeanne Carmen "Can't you just see me as First Lady?"
The book goes on to quote the late actor Pater Lawford, who married JFK's sister Patricia in 1954, as saying Monroe called Jackie to confess to the affair and to tell her that her husband had already agreed to leave his family and set up home with the actress.
Jackie is said to have responded, "Marilyn, you'll marry Jack, that's great. And you'll move into the White House and you'll assume the responsibilities of First Lady, and I'll move out and you'll have all the problems."
Other than the couple's relationship difficulties, the new book also claims the US President and his wife took regular amphetamine and steroid injections, administered by a man nicknamed Dr Feelgood.
Andersen claims the President took high-dosage shots around four times a week, a level believed to have concerned doctors due to the cocktail of medication JFK was already on to combat other health concerns.