Dave Grohl surprised fans when he joined Paul McCartney onstage Saturday night at the O2 Arena in London. He appeared unannounced midway through McCartney's headlining set; grinning, he joined McCartney to perform the Beatles hit "I Saw Her Standing There." The two previously performed together at the 2009 Grammy Awards, where they sang the same hit, according to Billboard.

The former Beatle began his set with a live debut of "Temporary Secretary," a cult favorite from his "McCartney II" album. He then brought out the former Nirvana member and Foo Fighters singer Grohl to join him onstage, according to Consequence of Sound.

Watch McCartney and Grohl jamming below: