Frank Sinatra’s romance with Marilyn Monroe came to a screeching halt after he learned of her dark past, entertainment journalist Charles Casillo alleges.

In a new episode of “The Killing of Marilyn Monroe,” the podcast host claimed that the blue-eyed crooner had planned on marrying the Hollywood star in the early 1960s before learning she suffered from suicidal thoughts.

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“Like many men, Frank Sinatra fell under her spell,” Casillo shared in the episode, as reported by Us Weekly on Tuesday. “He treated her like he had never treated any other woman. He was very protective of her.”

However, Sinatra’s plans to tie the knot with Monroe allegedly crumbled after he spoke with his attorney.

“He actually went to his lawyer and said, ‘I think I am going to marry Marilyn,’ and his lawyer talked him out of it,” insisted Casillo, who alleged the attorney convinced him that marrying America’s most famous sex symbol would destroy his career.

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“The lawyer said, ‘Don’t marry her,’” said Casillo. “'She’s going to commit suicide, and if she kills herself during the time that she is Frank Sinatra’s wife, you will go down in history as the man responsible for Marilyn Monroe’s death.”

According to the podcast, Monroe’s previous marriage to playwright Arthur Miller was doomed from the start. The couple was married from 1956 until 1961.

“Arthur Miller ran with a very intellectual crowd,” celebrity biographer Mark Bego shared in the podcast. “And then Marilyn was looked at by people in power as just being that movie star, that blonde bombshell, that sex goddess.”

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Us Weekly said “The Killing of Marilyn Monroe” aims to investigate the icon’s final days by analyzing her career, marriages and affairs. The 12-part audio documentary comes from the creators of the Natalie Wood podcast titled “Fatal Voyage: The Mysterious Death of Natalie.” An episode drops every Monday.

In 2015, The Telegraph reported James Kaplan published a book titled “Sinatra: The Chairman,” which provides a detailed account of the singer’s relationship with Monroe.

“There was no doubt that Frank was in love with Marilyn,” said talent manager Milt Ebbins in excerpts of the book.

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According to the outlet, Sinatra and Monroe met in 1954 while he was still married to actress Ava Gardner. They began a relationship in 1961, which lasted for several months.

“Yeah, Frank wanted to marry the broad,” Kaplan quoted Jilly Rizzo, Sinatra’s close confidante, in the book.

“He asked her and she said no.”

Kaplan wrote that a year later, in 1962, Monroe accompanied Sinatra to his Cal-Neva resort in Lake Tahoe. A week later, Monroe died at age 36 from a barbiturate overdose. Joe DiMaggio, who was previously married to Monroe from 1954 until 1955, turned Sinatra away from her funeral.

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In August 2018, Casillo, who wrote a book titled “Marilyn Monroe: The Private Life of a Public Icon,” told Fox News Monroe’s final years were tumultuous.

Monroe, who was battling crippling depression, anxiety and low self-esteem, was under the round-the-clock care of a psychiatrist. It was reported that around this time the actress was also struggling with substance abuse, as well as physical ailments, including endometriosis, which resulted in a public miscarriage during her marriage to Miller.

Then in 1962, Monroe, who was in the middle of filming “Something’s Got to Give,” was fired from the romantic comedy after she was consistently late or absent for days at a time. She would be found dead from an apparent overdose just two months later.

Casillo tracked down some of the last living people who befriended Monroe before her death.

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“She had been living a very chaotic and frantic existence in her last months,” he explained. “She was on a downward spiral… She was 36 years old, and for her, that was devastating… In that era, a sex symbol, a love goddess, like Marilyn was, to be 36 was considered to be at the end of her rope.

"For someone like Marilyn [whose] whole identity and whole persona came from being sensual… the idea of losing that was very frightening to her… Also on the last day, she was furious about a lot of things… She was very angry, she was very frightened.”

Casillo said that part of Monroe’s emotional turmoil stemmed from her life-long quest to develop a relationship with her father after enduring an erratic childhood in a series of foster homes where she was sexually abused, only to be brutally rejected.

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“She was born illegitimately and her mother was in and out of mental institutions,” he explained. “… Her mother would show her a photo of a man with a fedora, a handsome guy, saying, ‘This is your father.’ At that time, Marilyn was shuffled from one foster home to another.

"She was in orphanages. She felt like she didn't belong anywhere, and her father came to represent security and someone who would love her and take her away from the kind of miserable existence that she had.

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“… When she became an adult, she did try to contact him, and he wouldn’t talk to her. He wouldn’t see her. He said, ‘Talk to my lawyer.’ So he wouldn’t recognize her as being his daughter. I think that Marilyn spent her whole life trying to find a man to be a substitute for her father, someone who would be a savior, someone who would protect her, someone who would comfort the little girl that was always inside of her.”