Billionaire financier Leon Black suffered setbacks this week in a defamation suit brought against him by his former Russian mistress, with a judge ruling that he won’t be able to keep his ties to dead pedophile Jeffrey Epstein out of the case.

New York state Judge David Cohen ruled on Monday that he wanted to know more about the relationship between Epstein and Black — the former chairman and CEO of private-equity giant Apollo Global Management — in the ongoing lawsuit filed by Russian model Guzel Ganieva and a second woman who claims Black sexually abused her, according to a court filing.

The ruling means discovery can begin in earnest and — unless Black reaches a settlement with Ganieva, whose explosive Twitter posts about her relationship with Black came shortly before his surprise announcement last spring that he was stepping down as Apollo’s CEO — could face a salacious trial as soon as next year, according to court papers.

The suit centers on Ganieva’s allegation that Black defamed her after she alleged in a series of cryptic March 2021 tweets that she had been a victim of Black’s sexual abuse. In response, Black claimed that he and Ganieva had a consensual affair and alleged that she had extorted him, knowing that he wanted to hide the relationship from his family.

Ganieva then sued Black in June for defamation, and detailed multiple rape allegations. Her first complaint didn’t include any mention of Epstein. But as the two sides have battled, Epstein’s name has cropped up in newer, more detailed filings.

Ganieva has alleged Black once flew her to Florida to have sex with Epstein and that he raped another woman at Epstein’s Manhattan townhouse.

Black also said under questioning that Epstein was one of a handful of people who knew about her alleged threats of extortion against Black in 2015 when she allegedly demanded $100 million. That led to a confidentiality agreement, and Epstein was one of a few who knew about the details, which included Black paying Ganieva $100,000 a month for 15 years, according to court papers.

Judge Cohen not only struck down Black’s motion to get Epstein’s name removed from the case, but also that Ganieva’s allegations of sexual abuse were relevant despite his request to have them tossed.

“The underlying facts about Epstein are at the center of the material facts in dispute,” Judge Cohen said in the latest ruling. “Defendant [Black] was not merely ‘associated’ with Epstein, and Epstein is not a background figure in this case.”

“Thus, contrary to defendant’s repeated claims that Epstein had “nothing” to do with plaintiff’s allegations, such that the mention of Epstein’s name was a mere prejudicial diversion, the facts show that Epstein was significant to plaintiff’s claims in this case,” the judge added.

Black, Apollo’s co-founder, had claimed Epstein had no place in the Russian model’s defamation suit. A lawyer for Black in December said Ghislaine Maxwell’s trial served as a warning that the billionaire would not get a “fair shake” if his alleged ties to Jeffrey Epstein were not thrown out.

“If this completely horrifying and horrific stuff that has nothing to do with any of the facts of this case come in, then our client has no shot of getting a fair shake in this case,” Black’s lawyer Danya Perry told the judge.

“Ms. Ganieva’s lawsuit is and always has been a frivolous attempt to further extort Mr. Black,” Black’s lawyer Michael Carlinsky said in a Thursday statement. “The court’s procedural ruling last week allowing her to file yet another complaint does not change the fact that her claims are baseless. Documentary evidence shared in response to Ms. Ganieva’s allegations demonstrates beyond doubt she had a years-long consensual relationship with Mr. Black. Her allegations about Jeffrey Epstein were thrown into her most recent complaint in an obvious attempt to divert attention away from the actual evidence showing her claims to be complete fiction.”

Judge Cohen also ruled to allow Ganieva’s second amended complaint, which includes allegations of Black’s sexual abuse against another victim, named in the filing as Jane Doe.

Doe’s claims corroborate Ganieva’s story about Black’s alleged sexual violence, Cohen wrote, “as well as Black’s reliance on using money to attempt to buy the silence of his victims. The additional facts also provided more background about defendant’s personal relationship with Epstein.”

“Defendant [Black] also argues that the amended complaint is “replete with incendiary, inflammatory, and highly charged language” … and seeks to exclude all references to the sexual abuse he allegedly inflicted on plaintiff,” Judge Cohen noted.

“While these allegations are certainly personally embarrassing to defendant, they are nevertheless relevant to plaintiff’s claims.”

A main focus now, sources said, is for Ganieva to subpoena Black’s former executive assistant Melanie Spinella.

“You had to get through her if you wanted to speak to Leon,” a source said, referring to the close aide who knew everything about Black.

This is not the first time Black has unsuccessfully tried to whitewash his entanglement with Epstein.

In 2019, Black was forced to admit that Epstein was on his family’s foundation board for six years after he was convicted for soliciting a minor in Florida in 2008, following a report by The Post.

Black called it a clerical error and told Bloomberg: “Jeffrey Epstein resigned in July 2007 at the family’s request from the Leon Black Family Foundation and has not been affiliated with or performed any duties for the Foundation since that date.”

However, Apollo hired the law firm Dechert to conduct an internal investigation of Black last year and found he paid Epstein — who committed suicide in prison in August 2019 — $158 million between 2013 and 2017 for professional advice on tax audits, wealth management and estate planning.

In his Thursday statement, Black’s lawyer added, “The Dechert Report, following an exhaustive investigation by one of the most reputable lawyers and law firms in the US, completely discredits [Ganieva’s] allegations. We will vigorously defend Mr. Black.”

Black has since resigned as CEO and chair of Apollo, and as the chair of the Museum of Modern Art.