According to an explosive new book, Marilyn Monroe called Jackie Kennedy at the White House and confessed she was having an affair with JFK.

The First Lady responded: “That’s great… I’ll move out and you’ll have all the problems.”

In These Few Precious Days: The Final Year of Jack with Jackie, author Christopher Andersen claims Jackie Kennedy “knew everything” about JFK’s cheating and turned a blind eye, but his relationship with Marilyn Monroe “seemed to bother her the most”.

Jackie Kennedy was right to fear the bombshell actress, because Marilyn Monroe’s sights were firmly set on becoming the President’s second wife.

Marilyn Monroe, who long grappled with psychiatric and emotional problems as well as drugs and alcohol, was convinced JFK was about to leave Jackie Kennedy for her, her friend Jeanne Carmen reportedly revealed.

“Can’t you just see me as first lady?” Marilyn Monroe asked Jeanne Carmen.

Author Christopher Andersen claims Jackie Kennedy knew everything about JFK’s cheating and turned a blind eye, but his relationship with Marilyn Monroe seemed to bother her the most

According to excerpts of the book, published by The New York Post today, Peter Lawford claimed Marilyn Monroe called Jackie Kennedy and told her she was sleeping with JFK, and that he’d allegedly promised to leave his family for her.

“Marilyn, you’ll marry Jack, that’s great,” Jackie Kennedy responded, according to the account.

“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.”

Christopher Andersen writes JFK’s Air Force aide, General Godfrey McHugh, revealed early on that “Jackie knew about his women” and her friend Ralph Martin agreed.

“You know, in the end Jackie knew everything. Every girl. She knew her rating, her accomplishments . . .”

However, she didn’t take his cheating lightly.

JFK’s close friend, George Smathers, said Jackie was “damn mad” about his fooling around, but she was willing to look the other way as long as he was careful and didn’t humiliate her.

Jackie Kennedy reportedly feared her own s**ual inadequacies were pushing JFK into the arms of other women.

But she complained of the President’s love-making to her long-time confidant Dr. Frank Finnerty, claiming “he just goes too fast and falls asleep”.

Aside from the ladies, Christopher Andersen offers a fascinating insight into JFK’s dependence on drugs.

His physician Max Jacobson, known as Dr. Feelgood, administered high-dosage amphetamine shots laced with steroids to the president on a regular basis, the book claims, and even the first lady.

Dr. Max Jacobson’s four-times-weekly injections worried other physicians who believed they might react with the dozen or so other drugs JFK was taking for his other health woes.

Gore Vidal reportedly said he was “horrified” to learn Dr. Feelgood was treating the President and, according to the book, told Jackie Kennedy to “Watch out” because “Max drove several people mad”.