The ex-husband of killer mom Gigi Jordan filed a defamation lawsuit against her Thursday, saying her testimony at trial ruined his reputation.

The suit, filed in Manhattan federal court, came as Jordan was sentenced to 18 years behind bars for fatally poisoning her 8-year-old autistic son.

Raymond Mirra, 56, claims Jordan damaged his public image by testifying that he stole from her and threatened to have her killed because, she asserted, she knew he was connected to the Mafia.

“Ms. Jordan testified that she had poisoned Jude to death by feeding him over 50 pills of various prescription sedatives,” the lawsuit says.

“However, she attempted to mitigate her culpability by telling ludicrous falsehoods about Mr. Mirra that, she claimed, diminished her responsibility for taking Jude’s life.”

Manhattan Supreme Court Justice Charles Solomon blasted Jordan at sentencing Thursday, saying there was no possible basis for her claims that Mirra wanted to rob or kill her.

Jordan — who Solomon said is worth between $30 million and $50 million — also lied about Mirra on the “Dr. Phil” show and on her Web site gigijordan­truth.com, the lawsuit says.

Mirra is not Jude’s father.