Frank Sinatra Believed Marilyn Monroe Was Murdered, New Book Claims

Here are seven crazy facts about Marilyn Monroe on what would have been her 91st birthday. Here, she is pictured as a holographic image as part of an exhibit at Madame Tussauds in Tokyo, May 16, 2016.

Frank Sinatra didn't believe that Marilyn Monroe died from an accidental overdose, a new book has claimed.

Sinatra's close friend and former manager Tony Oppedisano wrote about the singer's suspicions about Monroe's death on Aug. 4, 1962, in his new memoir, "Sinatra and Me: In The Wee Small Hours.

"Frank believed she was murdered, and he never got over it," Oppedisano wrote in an excerpt published by People Wednesday.

The author claimed that the "My Way" crooner and "Gentlemen Prefer Blondes" star were close friends but had never been lovers. Sinatra found her beautiful and funny but "too troubled, too fragile, for him to sleep with and then walk away," Oppedisano wrote.

Despite this, Monroe apparently confided to Sinatra her intimate secrets, including her alleged affairs with John F. Kennedy and Robert F. Kennedy.

"Marilyn told Frank she didn’t understand why they’d shut her out completely once she stopped having sex with them," he alleged.

The weekend before Monroe's death, she stayed at Cal Neva Lodge, outside of Lake Tahoe, which was partially owned by Sinatra. The author claimed she was there to spend time with her ex-husband Joe DiMaggio, who was staying nearby. She allegedly had decided to make a press announcement the following week to confirm that they were officially getting back together.

However, the press conference sparked rumors that she would be exposing her alleged affairs with the Kennedy siblings, the book claimed.

"Frank said she'd never have spilled about the Kennedys because she still had feelings for [Jack]," Oppedisano wrote, adding, "Frank believed if the press conference hadn't been announced, she would have lived a lot longer."

Sinatra's attorney Mickey Rudin, who also worked with Monroe, also believed that she had been killed, the book claimed. Oppedisano wrote that Sinatra had "several sources" who told him the same story about Monroe's death, which was that "she’d been murdered with a Nembutal suppository and Robert Kennedy or the Mob was involved."

While none of these theories have been proven almost five decades after her passing, one thing Oppedisano is sure about was that her death haunted Sinatra until he passed away on May 14, 1998.

"Conspiracy theories abound and I can't lay them to rest," Sinatra's close confidant wrote.

"Sinatra and Me: In the Wee Small Hours" is set to hit shelves Tuesday.