"They haven't done it in at least a decade," says a source. "They thought it would be fun"

Credit: Tim Mosenfelder/Getty

Bush frontman Gavin Rossdale and No Doubt singer Gwen Stefani met and fell in love when their bands toured together in the ’90s.

On Saturday night, the married rockers reunited on stage to sing Bush’s hit “Glycerine” for a surprised holiday-concert audience.

Rossdale, 47, usually performs the song by himself until the rest of Bush joins him toward the end, but at L.A. Radio station KROQ’s 23rd Annual Almost Acoustic Christmas show at the Gibson Amphitheatre in Universal City, Calif., he was joined by an extra-special guest on the second verse: his wife.

“The place went crazy,” an audience member told PEOPLE after the show. “They shared a quick kiss after the performance and Gwen exited the stage while Gavin and his band stayed to finish their set.”

And the couple never looked better: Rossdale’s sleeveless T-shirt exposed his biceps, and Stefani, 43, wore a black mesh top that showed off her great abs.

“Bush was playing tonight, Gwen’s in town, and they haven’t done it in at least a decade,” says a source. “They thought it would be fun.”

Fun and flashback worthy: Check out how Rossdale and Stefani looked when they first met at the same event 17 years ago when their respective bands performed at KROQ’s annual holiday show in 1995.