An ongoing Foo Fighters joke has finally reached its natural conclusion: a surprise performance from Michael Bublé.

Throughout their most recent tour, the band has made a special effort to spotlight their new live drummer, Josh Freese, with a medley dedicated to the many artists he's worked with over the years. The list includes Guns N' Roses, Paramore, Blink-182, Avril Lavigne, Beastie Boys, Offspring, Nine Inch Nails, and, yes, Bublé.

Focusing on Freese's connection to the pop and jazz singer, Foo Fighters frontman Dave Grohl has made a habit of welcoming fans on stage to offer their rendition of Bublé's song "Haven't Met You Yet." But since no one seemed to know all the lyrics during the group's set at the Outside Lands music festival in San Francisco on Saturday, Grohl turned to a superfan.

"You know what? At the last couple shows, I always look out and someone's like, 'I know the Bublé song. I'll come up and sing it,'" Grohl told the crowd. But, he added, "Every time someone says they know this song, they don't know the f---ing song."

As the intro to the track played, Grohl pointed out a particular concertgoer holding an "I heart Bublé" sign. "Do you know the f---ing song?" the former Nirvana member asked. "Hold on, we got a superfan. He's got the 'I love Bublé!'"

As he made his way to the stage, the "superfan" turned out to be Bublé himself, who joined Foos to sing his chart-topping single "Haven't Met You Yet."

"This motherf---er better know the song," Grohl quipped early on, but towards the end of the performance he acknowledged the obvious by exclaiming in faux shock, "Oh my god, it's Michael Bublé! Wait, what?!"

He later addressed the crowd, offering more context. "I'm just gonna tell you something, and I'll make it f---ing quick because we don't have a lot of time," Grohl said. "For real, we've been doing that thing where people from the audience come up and say, 'I know the f---ing song,' and they walk up and they're like, 'I know the first verse.' They don't know it!"

Motioning to Bublé, he continued, "So this badass motherf---er — and I'm not even kidding — flew in today from Argentina to f---ing sing that song to you guys. Because there's no such thing as taking a joke too far."

Along with Bublé's "Haven't Met You Yet," the full Freese medley included Beastie Boys' "Sabotage," Devo's "Whip It," and Nine Inch Nails' "March of the Pigs."

Speaking to EW in 2009, the prolific drummer joked about his impressive résumé but lack of name recognition. "I work with famous people, but I'm kind of under the radar," Freese said. "I'm probably famous to the drummer kid that lives down the street from me, but that's about it."

Foo Fighters' released their latest album, But Here We Are, in June. Watch their Freese medley with Bublé above.

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