If you didn't catch the 'Late Show With David Letterman' last night, you missed one of the most interesting performances in recent history. Along with country star Zac Brown, Foo Fighters took to the 'Letterman' stage for a cover of Black Sabbath's eternally heavy 'War Pigs.'

Country music and heavy metal are polar opposites, and it's almost unbelievable to picture a country musician taking on the vocal parts of the Prince of Darkness, Ozzy Osbourne. However, Zac Brown nailed it, bringing Ozzy's signature nuances of blues and soul to the 'Letterman' performance. Foo Fighters frontman Dave Grohl also tackled vocal duties, getting into the grittier side of 'War Pigs.' Grohl recently lent his production skills to the latest Zac Brown Band album.

David Letterman was floored by the Sabbath cover. As soon as Foo Fighters and Zac Brown hit the final note of 'War Pigs,' Letterman showed his fanboy side as he repeated "Oh my God" and "How 'bout that?!" multiple times. "You have Zac Brown, Black Sabbath and Foo Fighters," Letterman began. "I don't know. What do you kids want from me?!"

Dave Grohl also spared a few minutes for an interview with Letterman, speaking about Foo Fighters' new album, 'Sonic Highways' and Grohl's daughter's affinity for Amy Winehouse and a certain rap song the Foo Fighters frontman didn't approve of. Check out both clips below.

The Sabbath cover acts as the launching point for Foo Fighters' week-long stint on the 'Late Show,' with a new performance hitting viewers every night until Oct. 17. Foo Fighters' HBO series on the recording of 'Sonic Highways' will debut on Oct. 17, so get your DVRs fired up for that. The 'Sonic Highways' record will hit stores on Nov. 10.

In even more Foo Fighters news, the band has collaborated with Facebook to celebrate the 'Sonic Highways' series premiere. Immediately following the premiere episode, Foo Fighters will perform a set at Chicago's Cubby Bear venue, where Grohl saw his very first punk rock show. Once episode one of 'Sonic Highways' airs, head over to HBO's Facebook page to stream the concert for free!

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