A retired NYPD sergeant who swore never to give a part of his pension to his ex-wife ​has lost his fight to keep the money for himself.

Lisa Giangregorio, who was married to ex-cop Sebastian Giangregorio for 18 years, got her first monthly payment Monday from the New York City Police Pension Fund — a check for $2,756.

The victory came a month after The Post told her story and a noted lawyer volunteered to help.

“First, I was shocked, then I was overjoyed and grateful,” said Lisa, a hairstylist who lives in Naples, Fla., with their three children.

Sebastian — who once vowed in an email, “If my lungs move, she will never get my pension” — ignored a 2017 order to pay Lisa half of his pension.

In October, a Florida judge ordered the NYPD fund to pay her directly. But Lisa was told she had to go to a New York court for the order to take effect.

She could not afford the legal fees, so New York divorce lawyer Jill Stone stepped in, pro bono, and had the order filed in New York Supreme Court.

Sebastian, of the Bronx, still owes Lisa $51,000 in pension back payments. In a text message Friday, he said he’d try to pay the debt but added, “Because of false allegations, how can I even earn a living, and your bogus story doesn’t help.”