Marilyn Monroe had sex with Bobby Kennedy 30 minutes before she sang ‘Happy Birthday’ to his brother JFK

President John F. Kennedy and his brother Bobby both had simultaneous affairs with Marilyn Monroe, a new book has revealed.

In ‘Don’t Ask: The Kennedys and the Women They Destroyed’author and DailyMail.com columnist Maureen Callahan describes the crossover relationships as an “incestuous sexual competition” between the two men.

Marilyn first met JFK — who was already married to Jackie — at a Hollywood party in 1954, Callahan writes, and in the years that followed the actress fell in love with both the president and his brother, who was also married.

The only known photo of Marilyn with both Bobby, left, and JFK, taken at a reception after her Garden performance.

Marilyn’s psychiatrist was very concerned about things and warned: ‘I’m trying to help her not be so lonely and […] becoming involved with very destructive people who enter into a kind of sadomasochistic relationship with her.’

On May 19, 1962, Marilyn sang “Happy Birthday” to JFK during her famous performance at Madison Square Garden.

But, Callahan reveals, just thirty minutes before she appeared on stage, she had sex with Bobby in her dressing room.

“They spent 15 minutes alone together,” Callahan wrote.

The liaison made her late to the stage, where she arrived “drunk and red from the transgressive sex she had just had with Bobby, her dress so tight she could barely walk.”

Jackie Kennedy was “furious” after the performance, leaving JFK “slack-jawed” in the audience. And so, Callahan writes, Jackie gave her husband an “ultimatum,” telling him he could no longer see Marilyn or “she would divorce him—take the kids and cost him a second term.”

JFK agreed and never slept with Marilyn again.

Her affair with Bobby continued, with Bobby even visiting her the night she died at her LA home, on August 4, 1962.

“The FBI and CIA, Bobby and Jack discovered, had tapped Marilyn’s home and phone line without her knowledge…Bobby did not leave without the tape recordings,” Callahan writes.

“Where the hell is it?” Bobby asked. But Marilyn had “no idea” what he was talking about.

On May 19, 1962, Marilyn sang “Happy Birthday” to JFK during her famous performance at Madison Square Garden. But, Callahan reveals, just thirty minutes before she appeared on stage, she had sex with Bobby in her dressing room.

Bobby left empty-handed and Marilyn’s body was found early the next morning by her housekeeper. “She was lying face down on the bed, naked, with her phone still in her hand,” Callahan wrote.

“Former senior FBI agent James Doyle later admitted that the Bureau had been ordered to delete certain phone records [from Marilyn’s home],” she adds. “Marilyn’s logs showed that she called Bobby’s workplace eight times between June 25 and June 30. Reports indicate she had an abortion on July 20 and the baby may have been Bobby’s.”

Marilyn’s second husband Joe DiMaggio banned both Kennedy brothers from Marilyn’s funeral.

“I always knew who killed her, but I didn’t want to start a revolution in this country,” DiMaggio reportedly said years later. ‘She told me someone was going to arrest her, but I kept my mouth shut.

‘Many Kennedys were murderers of women, and they always got away with it. In a hundred years they’ll get away with it.’

Callahan also reveals that in 1985, ABC News planned to air a special documentary about JFK and Bobby’s possible involvement in Marilyn’s death, but it was canceled just hours before it was scheduled to air.

The network’s then-president Roone Arledge, who “was a longtime friend of Ethel Kennedy” [Bobby’s wife]’, defended his decision by saying the special was ‘gossip column stuff’ and ‘doesn’t live up to the billing’.