Frank Sinatra was convinced Marilyn Monroe was murdered.

Marilyn Monroe

Marilyn Monroe

The iconic actress died in August 1962, at the age of 36, and according to a new book by Tony Oppedisano - Sinatra's close confidant and former road manager - he was sure she was murdered.

In 'Sinatra and Me: In The Wee Small Hours', an excerpt of which has been published by People, Tony shares: "Frank believed she was murdered, and he never got over it."

The Hollywood icon's death has remained a subject of intense speculation and conspiracy theories for decades. However, the coroner at the time time classified her death as probable suicide, after she took an overdose.

Sinatra and Monroe were close friends but were never lovers, according to the new book, which reveals that Sinatra found the actress to be beautiful and funny.

Tony explained: "Frank felt she was too troubled, too fragile, for him to sleep with and then walk away."

Marilyn had a string of high-profile romances during her life, including marriages to baseball legend Joe DiMaggio and playwright Arthur Miller.

And she was even happy to discuss her secret affairs with US President John F Kennedy and his brother Robert Kennedy with Sinatra.

Tony shared: "Marilyn told Frank she didn't understand why they'd shut her out completely once she stopped having sex with them."

The weekend before her death, Marilyn was set to call a press to announce she was rekindling her romance with Joe.

At the time, it was speculated that she was set to discuss her flings with the Kennedy brothers - but Tony insists that would never have happened.

He said: "Frank said she'd never have spilled about the Kennedys because she still had feelings for [John].

"Frank believed if the press conference hadn't been announced, she would have lived a lot longer."

Sinatra - who died of a heart attack in May 1998, aged 82 - revealed that several people had told him the iconic actress was the victim of a murder plot, rather than an overdose.

According to the book, he said: "She'd been murdered with a Nembutal suppository and Robert Kennedy or the Mob was involved."