JFK Assassination Documents Reveal RFK Was Worried About Book Relating To Affair With Marilyn Monroe 

Join People Perks and save up to $1,200 a year

From left to right: Robert F. Kennedy, Marilyn Monroe and John F. Kennedy in 1962

Cecil Stoughton/The LIFE Images Collection/Getty Images

According to the newly declassified JFK assassination files, President John F. Kennedy’s younger brother Robert F. Kennedy was sent a memo warning him about the impending release of a book detailing his “close relationship” with screen legend Marilyn Monroe.

The memo noted that a 1964 book by Frank Capell, 

, made frequent references to Monroe and RFK, then the U.S. attorney general.

“Throughout the book … Capell claims that you had a close relationship with Miss Monroe,” officials warned RFK in the document, according to Politico.

Before her 1962 death at 36 of a barbiturate overdose, Monroe was rumored to have had affairs with both RFK and JFK. In fact, some speculated that her alleged romances with the brothers may have played a role in her death, which was ultimately ruled a suicide.

It was reported at the time that Monroe had been threatening to hold a press conference divulging her relationships with the brothers.

RELATED VIDEO: Jerry Lewis on His Secret Love Affair With Marilyn Monroe

“What happened to Marilyn Monroe is one of the great mysteries of the 20th century,” her biographer James Spada told PEOPLE in 2012.

Though Spada doesn’t believe there’s any proof that the Kennedys were responsible for Monroe’s death, he said “it was pretty clear that Marilyn had had sexual relations with both Bobby and Jack.”

Further fueling the theory that the Kennedys were somehow involved in Monroe’s death are witnesses’ claims that they heard a disturbing tape, from the bugged Monroe home on the night she died, on which the voices of actor Peter Lawford, an angry Bobby Kennedy and a screaming Monroe are audible.

In a 1983 BBC interview that Monroe biographer Anthony Summers conducted with the star’s former live-in housekeeper, Eunice Murray, he said there was a “moment where she put her head in her hands and said words to the effect of, ‘Oh, why do I have to keep covering this up?’ I said, ‘Covering what up, Mrs. Murray?’

“She said, ‘Well of course Bobby Kennedy was [at Monroe’s apartment the night she died], and of course there was an affair with Bobby Kennedy.’ ”

1 The Most Shocking Revelations from the Newly Released John F. Kennedy Assassination Files

2 Donald Trump Accidentally Wished the Wrong Lee Greenwood a Happy Birthday on Twitter — and the Guy\'s Reaction Is Perfect

3 Kellyanne Conway Interrupts CNN Interview to Talk to a Squirrel

4 Donald Trump ‘Dishonored’ with Plaque Marking the Spot Where He Boasted About Grabbing Women

5 Rosie O\'Donnell Opens Up About Donald Trump: \'I Seriously Worry Whether I Will Be Able to Live Through His Presidency\'