Matt Damon and David Letterman shocked “Gilded Age” viewers with a blink-and-you-missed-it appearance during Sunday night’s Season 4 premiere.

More than eight minutes into the episode, the “Good Will Hunting” actor, 56, and the comedian, 79, portrayed gentlemen crossing the street without saying a word.

The camera panned over them to George Russell’s home, where Russell (portrayed by Morgan Spector) was recovering after getting shot at the end of Season 3.

Damon looked unrecognizable in the scene with faux sideburns and a mustache.

The “Odyssey” star rocked a top hat, a white shirt under a long black coat and a pair of slacks, while Letterman sported a bowler hat, a black long coat and slacks with his famous white beard on full display.

Social media users had a heyday with the surprise, with one tweeting, “I thought I was seeing things!!”

Another wrote, “I KNEW IT!!”

Vulture reported that the cameo stemmed from the former “Late Show” host’s “nearly 50-year-long quest to become a background actor.”

After several failed attempts, Letterman and his “My Next Guest Needs No Introduction” team began researching Damon, who kicked off his career as a background actor alongside Ben Affleck, for a future episode.

“We thought, ‘Okay, this could be the perfect opportunity,’” “My Next Guest” showrunner Isabel Richardson told the outlet.

“It’d be really fun for Dave to do this with Academy Award–winner Matt Damon, and it tied into [Damon’s] origin story really well,” she explained.

After a “My Next Guest” line producer soft-pitched the idea to a friend working on “The Gilded Age,” the idea was brought to Kate Churchill, the HBO show’s executive producer, who took the pitch to showrunner and creator Julian Fellowes, HBO head of drama Francesca Orsi and HBO CEO Casey Bloys.

“I have to really give credit to our studios because a simple idea was actually quite complicated,” Churchill shared with Vulture.

“Things like, Matt had to be paid as a background person, but of course he works under his own company,” she continued. “There were a lot of emails going around, but people really locked arms, and both studios saw that it was a fun collaboration where we could help each other.”

Neither Damon nor Letterman were credited for their background roles.

New episodes of “The Gilded Age” air on Sunday nights at 9 p.m. ET/PT on HBO.