In case you didn’t know, Foo Fighters are currently enjoying a five-day residency on the Late Show With David Letterman to promote their upcoming album, “Sonic Highways,” which will be out November 10th. They promised to perform new tracks each show, but last night they had a surprise in store for the lucky audience. Country star, Zac Brown, joined the band on stage to perform a cover of Black Sabbath‘s classic “War Pigs” and you can watch the performance here! Covering metal isn’t anything new to Zac, as he’s covered Metallica live before, but add in Dave Grohl‘s energy alongside Foo Fighters, and this performance sounded amazing! Enjoy it below!