James Dean was allegedly blackmailed by a gay ex-boyfriend who threatened to out the actor before his big Hollywood break, according to a new book.

Author Jason Colavito details the drama of Dean and Rogers Brackett’s troubled relationship in his new book, “Jimmy: The Secret Life of James Dean,” the Daily Mail reported Friday.

According to Colavito, Brackett pressured Dean to pay him $800 in 1954, just days before the actor’s 1955 film East of Eden premiered. The deal reportedly remained secret for seven decades.

The author claims that Dean shelled out the money despite his belief that Brackett sexually exploited him during their year-long affair.

Brackett believed Dean owed him, as Brackett allegedly paid $450 in hotel bills and more than $700 in gifts and loans to the actor when he was living in poverty in New York. Brackett also introduced Dean to many important people in the film industry and helped him gain success in his career.

Brackett, who had lost his advertising job and was short on funds while planning an opera with composer Alec Wilder, ended up approaching Dean for money, the author writes.

“Brackett forced Dean to have a drink and, striking a more conciliatory tone, asked him for money — a loan, he called it,” Colavito claims. “The insanity of the request shocked Dean, who had come to believe that his time ‘dancing’ for Brackett’s friends was abusive.”

“‘I’m sorry, pop,” he said to Brackett, refusing to give him money. He told her that he was over him, that he didn’t want to see him anymore. But in private he was angry.”

Wilder reminded Dean that Brackett had helped launch his career and asked the actor to write Brackett a letter of apology.

“The threatening public scandal under the current if Dean refused was obvious. (Wilder) blasted Dean for his insanity, asking Dean to write a letter of apology and yelling that Brackett should sue Dean for all the support he’s given him over the years.” , the book shows.

“I didn’t know the whore paid — I thought it was the other way around,” Dean allegedly yelled, according to Colavito.

After the allegedly explosive exchange, Brackett sent Dean a formal legal letter demanding that he repay Brackett the $1,200 he loaned Dean during their affair.

Colavito writes that the letter came with an implicit threat to expose Dean’s sexuality if he did not “liquidate his obligation.”

Brackett then sued Dean for $1,400 in New York Municipal Court, prompting Dean to quickly agree to a settlement of $800 (which would be equivalent to over $10,000 today) in weekly installments of 100 dollars, to avoid any gossip.

Brackett accepted the offer and Dean paid him the full amount. Dean’s agent also reportedly signed on to convince Warner Bros. to pay Brackett a large “search fee” to ensure his “continued silence,” the book says.

Copies of court documents included in the book show no evidence that there was an argument between the two sides, and simply show that Brackett and Dean reached an agreement.

“This story has never been told before and all parties involved worked hard to make sure no one ever found out,” Colavito told the Daily Mail.

“And for seventy years, nobody did. The only reason we know about it today is because Dean’s agent secretly kept copies of his files hidden for decades,” he added.

“Jimmy: The Secret Life of James Dean” will be available for purchase on November 19.