The revelation came in a new book by Christopher Anderson called These Precious Few Days: The Final Year of Jack with Jackie.
While no one is shocked to hear that President Kennedy had an affair with the blonde bombshell, her bold call to the First Lady was new information.
During the call Monroe was said to have told Mrs. Kennedy that the president was going to marry her before his term was up.
How did Jackie respond?
"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" reports AFP.
Julie Miller of Vanity Fair calls that "Point: Jackie."
Anderson’s work claims the First Lady knew about the president’s affairs and was generally unconcerned.
But he says Monroe did worry her because she understood the national fallout if the scandal became public.
Mrs. Kennedy was also more uneasy about the movie star due to Monroe’s certainty she would soon marry the president.
“Can’t you just see me as first lady?” Marilyn was said to have asked a friend.