“Uncut Gems” has unearthed a real Diamond. The Oscar-buzzy Adam Sandler thriller stars Garment District legend and first-time movie actor Wayne Diamond.

Retiree Diamond — who has a Bikini Atoll tan, a majestic silver blowout and veneers that are not so much pearly whites as pearly floodlights — tells Page Six that he befriended one of the movie’s producers, Sebastian Bear-McClard (a k a Mr. Emily Ratajkowski), at the Spotted Pig nearly a decade ago.

When the project got off the ground a couple of years ago, the producers called Diamond about a major role in the flick.

Diamond tells Page Six that — by way of a chance meeting with the so-called mob’s accountant, Meyer Lansky — he got into the dress-design and -manufacture business, and became one of its leading figures in the ’80s.

Diamond says he retired around 2000 after making millions — and losing some of it as “the second-best gambler in New York” — and took up acting.

“Uncut Gems” is his first feature, after making a few music videos and shorts. But the Long Island-born Diamond, who now lives on the Upper East Side, tells us that his time as a dressmaker prepared him for Hollywood.

“Go sell f - - king dresses. If you’re [a salesman and you’re] not a good actor, you’re not making a lot of money; you’re not selling a lot of dresses,” he said. “It’s all, ‘You’re gorgeous, I love you so much, let’s go out for a drink. I’ll f - - k you just so you’ll write me an order.’ My whole life was like that until I became someone.”

And now, he says, “I could be in an Academy Award-winning movie! F - - k you! Your odds are a billion to one of being in an Academy Award-winning movie!”

Meanwhile, he recalled to us that, through his Lansky connection, notorious lawyer Roy Cohn represented him in his divorce from his first wife. “He was the lowest of the low. The things he wanted to do to my wife. He said, ‘We’re going to wire the house.’ Unbelievable.”