Foo Fighters play with Michael Bublé after he flew from Argentina to the US to join them

Michael Bublé has joined the Foo Fighters onstage to perform his song 'Haven't Met You Yet' as part of a long-standing joke at the expense of the band's new drummer, Josh Freese.

Freese, who was a well-known session drummer before joining the Foos full time this year, has played with the likes of Guns N' Roses, Paramore, Blink-182, Avril Lavigne, Beastie Boys, Offspring, Nine Inch Nails, and Bublé himself.

As part of their recent tour, the Foos have been inviting superfans to sing Bublé's hit song on stage with them - but many who've taken up the challenge have been unable to remember the words.

However, that changed at the Outside Lands music festival in San Francisco on Saturday (local time), when lead singer Dave Grohl brought up a new 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. 

"Every time someone says they know this song, they don't know the f***ing song."

As the intro began, Grohl spotted a concert-goer holding an "I heart Bublé" sign and invited him on stage, asking: "Do you know the f***ing song? Hold on, we got a superfan. He's got the 'I love Bublé!'" 

That concert-goer was Bublé himself.

"This motherf***er better know the song," Grohl said, before adding: "Oh my God, it's Michael Bublé! Wait, what?!"

"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 went on. 

"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!" 

"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."

As video of the event circulated on social media, many fans were left stunned by the new musical collab.

"Michael Bublé joined Foo Fighters on stage to sing Haven't Met You Yet and my tiny mind just can't take it," one said on Twitter.

"Michael Buble just popped up in the middle of Foo Fighters' set because why not?" another wrote.

"Not Michael Bublé flying in from Argentina to sing with Foo Fighters," a third wrote.