Firefly Music Festival fans who caught the Foo Fighters’ headlining set were treated to a surprise during the band's cover-filled encore on Friday night.

Dave Grohl and the group covered a series of classic songs onstage -- including Queen’s ‘Under Pressure,’ the Rolling Stones’ ‘Miss You,’ Van Halen’s ‘Ain’t Talkin Bout Love’ and Alice Cooper’s ‘School’s Out’ -- at the Delaware-based festival.

“We’re gonna do something we’ve never done before,” Grohl told the audience before launching into the covers. “For the next 20 minutes, we’re a bar band called the Holy S---s that plays classic-rock songs.”

You can check out clips of some of the songs above and below.

The main part of their set was filled with 16 of the Foo Fighters’ own classic tunes, including 'Times Like These' and 'Monkey Wrench.' Notably absent was any new material from the album the band is currently working on and is scheduled for release in November.

Even though Firefly is the only date the band has on its concert schedule, they’ve also agreed to a TBD date in Richmond, Va., spurred by a team of dedicated fans’ crowdfunding campaign.