Unlike other celebrities and politicians who have allowed sexual assault accusations to ruin their careers, attorney Alan Dershowitz is fighting back early — and hard.

Dershowitz, a Harvard Law professor and outspoken critic of how colleges have been handling sexual assault, was accused of having sex with an underage girl by a former witness against billionaire investor Jeffrey Epstein.

Dershowitz categorically denied the allegation, calling it “totally, unequivocally and completely false.”

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The woman, identified in court papers as Jane Doe #3, made the allegations last Tuesday against Dershowitz and several prominent Europeans — including Britain’s Prince Andrew.

Jane Doe #3’s complaint accuses Dershowitz and others of taking part in Epstein’s transgressions. Her lawsuit accuses federal prosecutors in Florida of violating the law by not consulting with Epstein’s victims before arranging a deal requiring the investor to be sentenced to 18 months in prison.

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Jane Doe #3 mentioned several occasions in which she allegedly had sexual relations with Dershowitz. Dershowitz says he has documentation to prove he couldn’t have been in the same place as Jane Doe #3 at the times she claims, except once. And in that one instance, he was there with his family.

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"I'm planning to file disbarment charges against the two lawyers who signed this petition without even checking the manifests of airplanes or travel itineraries, et cetera," Dershowitz told Politico. "I'm also challenging the young woman and the lawyers to level those charges against me outside of the courtroom, so that I can sue them for defamation. ... Finally, I’m challenging the woman to file criminal charges against me because the filing of false criminal charges is a crime."