Billionaire investor Leon D. Black alleges that a woman who has accused him of sexual assault has extorted him for more than $100 million and defamed him and that she has formed a conspiracy with prominent employment and civil rights firm Wigdor LLP to take him down.

Black’s lawsuit was filed Thursday by attorneys from Quinn Emanuel Urquhart & Sullivan in the Southern District of New York, though he has made his claim that he is the victim of an extortion scheme by Russian model Guzel Ganieva—with whom he alleges he had a consensual and “regrettable” relationship with from 2008 to 2014—in earlier public statements.