Pop star Ed Sheeran performed his upcoming album at a VIP gig at the historic Kings Theatre in Brooklyn on Monday, with producer Aaron Dessner.

And we hear that insiders were surprised about the location of the after-party.

Rather than any chichi Manhattan nightclub, the celebration went down at O’Keefe’s pub near Downtown Brooklyn.

The Brooklyn Heights watering hole is better known as a hangout for Court Street lawyers and nearby St. Francis College students than celebs.

A source told us Sheeran was at the bar from about 10:15 p.m. till midnight with VIPs from the show, drinking Guinnesses and lagers as ESPN’s “SportsCenter” played on flat-screen TVs.

A local told us of O’Keefe’s usual scene, “It used to be a down-market Irish bar where cops would hang out during the day until they had to appear in a nearby courtroom.”

But years ago, “it spiffed up, added more and better beers, and a pub menu and a bunch of flat-panel TVs. It became something of a sports bar for St. Francis College students and Court Street lawyers at happy hour.”

While in town, Sheeran was also seen in a NYC subway station surprising a celebrity busker who was doing a rendition of the ginger-haired Brit’s newest single, “Eyes Closed.”

Reports said that “America’s Got Talent” alum Mike Yung was putting on a subway performance, and that Sheeran surprised him while Yung was crooning the singer’s latest hit tune.

They then did a duet together.

Sheeran has previously posted on Instagram of the ditty, “This song is about losing someone, feeling like every time you go out and you expect to just bump into them, and every thing just reminds you of them and things you did together… You sorta have to take yourself out of reality sometimes to numb the pain of loss, but certain things just bring you right back into it.”

The new album, “Subtract,” drops May 5.