Watch Paul McCartney and Dave Grohl Perform 'I Saw Her Standing There'

Beatle's London concert also features the first ever live performance of "Temporary Secretary"

Paul McCartney reunited with his "Cut Me Some Slack" pal Dave Grohl Saturday night when the Foo Fighters frontman made a surprise appearance onstage at McCartney's London concert to perform the Beatles classic "I Saw Her Standing There." While past collaborations between the two rockers have seen Grohl sit behind the drum kit, on this occasion the Foo Fighter joined McCartney up front and center at the O2 Arena to play guitar and sing on the chorus, NME reports.

However, the Grohl cameo wasn't even the biggest surprise from Saturday night's show: For the first time ever, McCartney performed McCartney II's frantic, synth-driven, krautrock-inspired "Temporary Secretary," a track that was never played live in the 35 years since its release. In its live debut, "Temporary Secretary" sounded remarkably fresh and faithful to the original. The song, which Rolling Stone dubbed both "an insane highlight of McCartney II" and "one of 12 weirdest Paul McCartney songs," continues a theme of dusting off old classics this tour, as we've also seen McCartney's solo live debut of the Beatles' "Another Girl."

McCartney and Grohl first performed "I Saw Her Standing There" together at the 2009 Grammy Awards, with Grohl serving as drummer for that encounter. The two linked up again – this time with Nirvana bassist Krist Novoselic and Foo Fighters guitarist Pat Smear – to record the Grammy-winning "Cut Me Some Slack" for Grohl's Sound City documentary.

"It was magic for me playing with these guys," McCartney told Rolling Stone of the collaboration in January 2014. "I knew who Dave was because I'd met him, and he said 'I have a couple of friends coming along.' And during the session I hear them talking: 'Wow, we haven't played since Nirvana.' So I found myself in the middle of a Nirvana reunion." Asked at the time if he and Grohl would perform together again, McCartney admitted, "You never know."

McCartney will play the second of two O2 Arena shows Sunday night in London.