A split image of Michael Bublé smiling into a microphone and Dave Grohl playing a white, electric guitar.

Michael Bublé joined Dave Grohl of the Foo Fighters onstage at Outside Lands in San Francisco.
(Scott Garfitt / Invision / AP; Amy Harris / Invision / AP)

Dave Grohl was the ultimate pretender this weekend while acting like he didn’t know Michael Bublé was going to join him onstage during Foo Fighters’ Outside Lands set.

Bublé made a surprise cameo Saturday during the rock band’s show at the San Francisco music festival as part of a long-running gag involving his 2009 single, “Haven’t Met You Yet.”

At recent Foo Fighters concerts, frontman Grohl has been asking fans if they know the words to “Haven’t Met You Yet” while introducing the crowd to drummer Josh Freese. The percussionist — who has been touring with the band since its longtime drummer, Taylor Hawkins, died last year — has played drums for a number of artists, including Bublé.

“The last couple shows — I always look out [into the crowd] — someone’s like ‘I know the Bublé song,’ ‘I’ll come up and sing,’ ‘I know the f— Bublé song,’” Grohl told the crowd at Outside Lands.

“And every time someone f— says they know the song, they don’t know the f— song. Do you know the f— song? Who knows the f— song?”

On cue, Bublé frantically waved from the audience while holding a sign that read, “I [heart] Bublé.”

“Hold on a second — we got a super-fan,” Grohl said, staying committed to the bit as Bublé approached the stage. “This motherf— better know the song.”

Without missing a beat, Bublé stepped up to the mic and began singing the first verse of the song with Freese on drums.

“OK, this guy’s pretty good,” Grohl joked. “This guy’s pretty good.”

While Bublé mostly performed the vocal part solo, Grohl chimed in at the very end, changing the lyrics on purpose from “I just haven’t met you yet” to “I just haven’t f— you yet.”

“Oh my God, it’s Michael Bublé!” Grohl exclaimed in mock-surprise before finally breaking character and giving the Canadian musician a proper shout-out.

“This bad-ass motherf— flew in today from Argentina to f— sing that song to you guys,” Grohl said. “‘Cause there’s no such thing as taking a joke too far.”

Foo Fighters headlined Outside Lands this weekend along with Kendrick Lamar and Odesza. Other acts from Saturday included Lana Del Rey, Maggie Rogers, Fisher, Father John Misty and Conan Gray.