Video: Paul McCartney and Reunited Nirvana Perform New Song, "Cut Me Some Slack"

Last night, as advertised, Paul McCartney was joined onstage at the 12-12-12 benefit concert by the surviving members of grunge giants Nirvana — Dave Grohl, Krist Novoselic and live guitarist Pat Smear.

Instead of Sir Paul leading the band through a medley of Bleach tunes, McCartney donned a slide and a Baratto cigar box guitar for a new song called "Cut Me Some Slack." You can watch footage of the performance below.

"Recently some guys asked me to jam with them," McCartney said, before being joined by Grohl and crew. "So I showed up like you do, ready to jam. And in the middle of it these guys kept saying, 'We haven't played together for years.' Then it finally dropped... I finally understood I was in the middle of a Nirvana reunion."

Grohl, Novoselic and Smear haven't performed live together in more than 18 years.

Other performers last night included The Rolling Stones, The Who, Bruce Springsteen, Bon Jovi and Roger Waters, who was joined late in his set by Pearl Jam frontman Eddie Vedder, who contributed to a stirring rendition of the Pink Floyd classic, "Comfortably Numb."

All of the proceeds from last night's show will go to benefit the Robin Hood Relief Fund, which is still working to help the victims of Hurricane Sandy. For more information on how to donate, head here.