The once-defiant Knicks turncoat who infamously sold his “fanhood” on eBay in 2018 after too many years of agita admits he’s finally hit his limit — and that his ex-team’s NBA Finals win has him sick with remorse.

Evan Perlmutter, 40, told The Post even as recently as last month — after the Knicks made it to the finals — that he had “zero regrets’’ about selling his loyalty to the highest bidder for $3,450 eight years ago and overnight switching his hoops loyalties to the Boston Celtics.

But Monday — two days after the Knicks sensationally beat the Spurs to capture this year’s NBA crown — Perlmutter said he’s become a basket case and can’t hold it in any longer.

“If you would have told me we’re definitely going to win one [championship] within ten years, then that obviously maybe changes things. Hindsight is 20/20,’’ the sports-marketing exec told The Post.

While not admitting he had “regret,’’ Perlmutter said, “It’s more remorseful.’’

Add to that “anger and disbelief.’’

As friends torment him for bailing on their hometown team, Perlmutter said, “To miss being part of history sucks.”

Not to be able to enjoy the moment” with childhood “inner circle” friends is “regretful,’’ too, he said.

A pal acknowledged to him that the moment must be “bittersweet.’’

Perlmutter shot back, “It’s just bitter, nothing sweet.”

He said it’s too hard to look at his phone or even attempt to bask in the ecstatic feeling in the city awash in a sea of blue and orange pride.

“I’m here biting my lip and getting aggravated,” he said. “There’s a different energy in the air in New York — an energy feeding off each other.

“Everyone in New York has this bond — it’ s very difficult to be a New Yorker and be against all of your peers. It’s a tough environment.

“Everybody’s walking a little taller, shoulders back. And I’m the Grinch over here.”

Still, he said of his fated decision nearly a decade ago, “People called me a fairweather fan who didn’t care.

“But the truth is, I cared too much. I was consumed by a team that couldn’t make competent decisions. It was like staying in an abusive relationship.”