Gianni Russo, the actor who played Carlo Rizzi in the iconic film “The Godfather”, has claimed in his new memoir, “Hollywood Godfather”, that he knows who killed Marilyn Monroe.

Russo was 16 years old when he began a four-year affair with the actress who was 33 years old at the time.

He also claimed that his involvement with the mob made him privy to sensitive information, such as the real reason behind Monroe’s death.

Russo said that he has photographic evidence of himself with Monroe, taken three days before her death, and that Chicago crime boss Sam Giancana took the photo.

Russo claims that the mob had convened at the CalNeva Lodge, a resort on the California-Nevada border, in hopes of setting a trap for President John F. Kennedy and his brother Robert, then the US attorney general.

According to Russo, key members of the mob had planned to film the Kennedys in a threesome with Monroe, with the aim of using the footage to blackmail JFK into invading Cuba and returning the island’s casinos to organized criminals.

The plan was allegedly scuttled after JFK did not show up. Russo claimed that Monroe had fallen in with the mob while courting favor with JFK years before.

When she learned of the aborted CalNeva scheme, she threatened to go to the media, and this led to her death.

Russo insists that it wasn’t the mob that killed Monroe, but rather the younger Kennedy, who feared the story of his and JFK’s involvement with Monroe going public.

“It had to be Bobby,” said Russo.

“No one else would kill her. The mob would not have done it. They liked her. She was that party girl. Give her a couple pills, a couple drinks and she’ll f–k everyone.”

Russo’s book also contains stories of his involvement with the mob.

He claimed that the late John Gotti, former boss of the Gambino crime family, saved his family’s lives. Russo said that the Colombian kingpin, Pablo Escobar, wanted to murder his family in retribution.

Russo got Gotti to set him up to meet with Escobar in Colombia, and he expected to take a beating or face death to save his family.

Escobar’s men tied him to a chair and roughed him up.

Then Escobar walked in, carrying ‘The Making of the Godfather’ book. He said, ‘Why didn’t you tell me you played Carlo Rizzi?’ … He let me go in exchange for me re-enacting one of my scenes, with him playing Michael Corleone.”

In addition to these claims, Russo also shared details of his wild lifestyle, which included threesomes with Liza Minnelli after both took a liking to the same Vegas showgirl.

Russo also had scrapes with Frank Sinatra, and while watching a western with Elvis Presley, Russo took cover as the King mimicked the on-screen pistol play with real guns.

Russo made a good living as a utility player for the mob, monitoring Vegas cash skims and laundering millions through the Catholic Church’s bank in Vatican City.

When Russo landed his role in “The Godfather,” it did not happen via normal channels.

After director Francis Ford Coppola announced his plan to turn Mario Puzo’s novel into a movie, there was pushback from the American-Italian Anti-Defamation League.

The group, overseen by Brooklyn mobster Joe Colombo, worried about the 1972 movie making Italians look bad.

Threats were made that film unions in New York City, where the movie film was to be shot, would not cooperate with the production.

Looking to leverage the discord, Russo showed up at Paramount’s New York headquarters and strongarmed his way into brokering a deal between Colombo and studio brass.

After reading the movie’s script, Colombo agreed to sanction “The Godfather” in exchange for Paramount allowing the Anti-Defamation League to put on a for-profit gala in every city where the film premiered.

In return, Russo claims, he was given the role of Carlo Rizzi, abusive husband to Connie Corleone.

He did not arrive quietly. “I wore Brioni suits to the read-throughs while all the other actors dressed like slobs,” said Russo.

“I hired a Chinese showgirl to drive me there in a Bentley. Everybody else took station wagons.”

Unimpressed, star Marlon Brando voiced concerns that the neophyte actor would screw up his movie. “I’d just had a party … celebrating getting [the role],” said Russo.

“This guy was going to destroy it for me? It would not happen.”

According to Russo, he got in Brando’s face and menacingly told the older actor, “Who the f–k are you to try to do this to me? I’ll cut your f–king heart out, you rat motherf–ker. I’m part of this picture whether you like it or not, you c–ksucker.”

The two became friends — a relationship cemented by Russo setting up Brando with the showgirl chauffeur, who took up residence in the latter’s hotel room.

The icon provided the beginner with acting lessons that contributed to Russo snagging small roles in 46 movies (including “Every Given Sunday” and “Sea Biscuit”).

They were tight enough that Russo was the first person Brando called in 1990 when tragedy unfolded at the screen legend’s Hollywood Hills mansion.

“Christian [Brando’s then-32-year-old son] had just fatally shot his sister Cheyenne’s boyfriend,” recalled Russo.

“I said, ‘Don’t call the police.’ Then I phoned [lawyer] Robert Shapiro and they got Cheyenne out of the house.”

Christian served five years for the murder and Brando kept himself from being implicated. “The shooting was done with Brando’s gun,” Russo said.

“Christian had told him that Cheyenne was getting beaten up and Brando said, ‘You’re her brother. Kill the son of a bitch.’ He probably didn’t expect Christian to do it.”

Sixty-three years after his chance encounter with crime king Costello, Russo ranks among the few golden-age mobsters who aren’t dead or in jail.

But he knows that whatever he does, he’ll always be known for his portrayal of a gangster on screen.

Indeed, when the waiter at Patsy’s serves dessert on the house, Russo can’t help but quip, “‘Leave the gun, take the cannoli.’ I can’t get away from that movie.”