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Necessity is the mother of pretension.

In a desperate bid for leniency at his upcoming sentencing, tax cheat and former congressman Michael Grimm — a man once caught on tape threatening to throw a reporter off a balcony — gave the judge a note from his mommy.

Even the woman who used to change his diapers admitted her boy made a boom-boom when he concealed from the tax man income from a restaurant he owned, but she asked that her only son be judged as an ordinary private citizen — rather than a former lawmaker and law-enforcement officer who should have known better.

“I am begging you to consider my son’s sentence based on his entire life, not just the one mistake and to make a sincere effort to ignore the politics, the speculation, and extreme negativity which have plagued the case before you,” mom Patricia Grimm wrote in a June 19 letter to Judge Pamela K. Chen. “My son certainly made a big mistake, and I strongly believe that he should be judged as any other restaurant owner would be, and has previously been, and not more severely because he later chose to dedicate his life to public service.”

But his mother’s plea to treat Grimm like a regular Joe flies in the face of efforts by his attorneys to play up his public service as a G.I. Joe. His lawyers submitted a copy of his honorable discharge from the Marine Corps alongside the plea from his mother.

Grimm copped to tax fraud on Dec. 23 in a plea deal to avoid a trial another 19 charges, including tax fraud, hiring undocumented workers, and lying under oath.

He stepped down on Jan. 5 — just weeks after the indicted legislator sailed to re-election against former Coney Island councilman Domenic Recchia.

Grimm, an attorney and retired agent of the Federal Bureau of Investigation, lost his federal pension and could be disbarred for his crimes, according to a letter he wrote to Chen. He faces up to three years in prison and a maximum fine of $100,000.

For their part, prosecutors say the former lawmaker, ex-Marine, and seasoned federal investigator should have known better.

“Grimm made the choice to go from upholding the law to breaking it,” said then-U.S. Attorney Loretta Lynch — now Attorney General — in a 2014 statement announcing Grimm’s indictment. “In so doing, he turned his back on every oath he had ever taken.”

Grimm’s sentencing is set for July 17.