One of the great moments of every Paul McCartney concert is when he counts off "1-2-3-4!" and launches into "I Saw Her Standing There." Last night (May 23), fans at London's O2 Arena got an even bigger thrill, when Dave Grohl joined him for the Beatles classic.

As you can see in the video above, Grohl played rhythm guitar and shared a mic with McCartney on background vocals. The song was performed in its traditional spot, at the end of the first encore.

Grohl and McCartney have been seen together a bit over the past few years. In 2012, they wrote and recorded "Cut Me Some Slack" with the surviving members of Nirvana for Grohl's Sound City documentary, and gave it a live debut at the 12-12-12 Hurricane Sandy benefit concert. The track won a Grammy for Best Rock Song.

And while McCartney singing "I Saw Her Standing There" wasn't a shock -- even if Grohl's guest appearance was -- he did have a few surprises in store. The set featured the U.K. debuts of "Another Girl," a deep cut from Help! and "Hope for the Future," the track he released last December for the Destiny video game. He also gave the world premiere to another album track, "Temporary Secretary," from McCartney II. We have no proof, but we'd like to think that McCartney decided to break it out after reading our recent feature about the album's 35th anniversary.

McCartney will perform a second show at the O2 tonight. His next U.S. date will be on July 31 in Chicago for Lollapalooza.

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