Fans who attended Lady Gaga's Las Vegas show Saturday night were treated to a star-studded surprise when Bradley Cooper appeared onstage — and the pair sang the duet, "Shallow," from their hit movie "A Star is Born."

Cooper, who starred in and directed the 2018 film, was attending a performance of Lady Gaga's "Enigma," one of two shows in her Las Vegas residency at Park MGM resort, when she apparently called him out of the crowd.

"So a really good friend of mine ... I don't know if you know him, but his name is Bradley. He made that movie, 'A Star Is Born,'" Lady Gaga said in a video posted to YouTube. "So, I'm gonna be a little chance-y .... Yo Bradley, you wanna come up and do this one?"

The audience went wild as Cooper reluctantly joined Lady Gaga next to her piano and sang the Golden Globe-winning duet.

The stars, who play Ally and Jackson Maine in the flick, had never belted out the song together in front of a live audience outside of the movie, reports Rolling Stone. However, it is likely the pair will be asked to perform at the Academy Awards next month.

"A Star is Born" is up for eight Oscars, including best picture, original song and best actor and actress nods for both Cooper and Lady Gaga.