Foo Fighters jam with Michael Bublé during Outside Lands headlining set

ABC/Randy Holmes

Foo Fighters‘ headlining set at the Outside Lands festival on Saturday, August 12, featured a surprise appearance by Michael Bublé.

As for why the Canadian crooner showed up during a Foos show, Rolling Stone explains that Dave Grohl and company have been performing a medley on their current tour, which features bits of new drummer Josh Freese‘s past collaborations with artists including Bublé. Their Bublé song of choice has been the track “Haven’t Met You Yet,” which Grohl has invited fans to sing onstage during recent shows.

In a clip from the Outside Lands performance posted to the Foo Fighters Facebook, you can see Grohl spot someone in the crowd holding a sign that read, “I [heart] Bublé.” That person turned out to be the real Michael Bublé.

Bublé also shared an Instagram video of him backstage with Grohl, excitedly sharing, “Well, the time has finally come: I’ve been asked to be in the Foo Fighters!”

“F*** you, Bublé!” Grohl responds.

FYI: Bublé is something of a rocker when it comes to the music he listens to; he’s especially a big fan of Deftones.