Last Friday, President Trump fired off two tweets containing a mysterious quote that passionately denounced the Democrats’ impeachment plans.

The opinion wasn’t from a powerful politician or a well-known pundit — it was from someone who Trump identified only as “Richard Ketay.”

Trump’s 65 million followers had never heard of him. Some wondered who he was — and others even doubted his ­existence.

But it turns out Ketay is very real — he’s an 85-year-old New Jersey retiree who wrote the comments backing Trump in a letter to the editor to The Post, which was published in the paper’s print edition last Thursday.

He couldn’t be happier to have been recognized by the president.

“Thank you, Mr. President,” Ketay told The Post from his Newark home on Monday. “I’m happy that he saw it and that he put it on Twitter and that other people read it.”

Ketay, who said he’s a former investigator with the Manhattan DA’s Office, admitted he doesn’t have his own Twitter account and didn’t know he had earned a shout-out from the commander in chief until The Post reached him at home.

In his letter quoted by Trump, Ketay wrote: “It isn’t often I get angry at the dirty politics of the Democrats in Congress, but this time I am enraged and hope this impeachment charade will backfire on Reps. Nancy Pelosi, Adam Schiff and all Democrats. I have read, thoroughly, the telephone conversation between Trump and the president of Ukraine and cannot find any reason to charge the president with high crimes and misdemeanors. This is just a phony witch hunt, perpetuated by Democrats to get rid of Trump because they cannot beat him in a fair election. Richard Ketay.”

Ketay, an ex-Democrat who switched to the GOP when he voted for Richard Nixon in 1968, says he has followed Trump’s career from day one, adding: “I was always interested in what he had to say.”

Ketay is a regular letter writer to The Post, previously calling for strong assault-weapons laws and describing the Senate hearings for Supreme Court nominee Brett Kavanaugh as a “farce.”

“I always speak the truth. My feelings are always in my letters, and in this particular case I was really angry at what the Democrats are doing — or trying to do anyway,” Ketay said of the impeachment inquiry.

Letters to the editor are not published online, which means Trump would have been flicking through the paper when he saw the comments on Page 26.