Watch Paul McCartney Perform 'Get Back' With Alabama Shakes' Brittany Howard

Rocker also delivers live solo debut of "FourFiveSeconds" at Lollapalooza

Paul McCartney served as Lollapalooza's headliner Friday night in Chicago, and the former Beatle had a special guest in the store to help him out during the encore: Alabama Shakes' Brittany Howard, who joined McCartney for a rousing rendition of "Get Back." The Sound & Color band had performed at the Chicago fest earlier in the day.

Howard contributed her unmistakable voice to the Let It Be track's second verse and shared chorus duties throughout with McCartney. During a false stop in the outro, McCartney and Howard delivered a little call-and-response. "Hey Brittany, you wanna get back?," McCartney asked, with Howard replying, "Let's get on back home, Paul." The rollicking outro picked up again full speed with McCartney and Howard trading off on vocals.

Howard's cameo wasn't the only surprise in McCartney's headlining set. Seven months after McCartney, Kanye West and Rihanna first unveiled their collaborative single "FourFiveSeconds," the rocker performed that song live for the first time solo. On an acoustic guitar, McCartney tackled the track's opening verse and chorus before launching into the Beatles' classic "We Can Work It Out."

McCartney's mammoth 32-song Lollapalooza set spanned his entire discography, from early Beatles hits like "Can't Buy Me Love" and "And I Love Her" to "Save Us" and "Queenie Eye" from his 2013 solo LP New. The concert was also, as of now, McCartney's last scheduled gig of 2015, wrapping up this leg of his long-running Out There tour. This jaunt also included visits to Delaware's Firefly fest, a surprise Dave Grohl appearance and the live debuts of McCartney II's "Temporary Secretary" and his first solo performance of the Beatles "Another Girl."

Lollapalooza continues Saturday at Chicago's Grant Park with Tame Impala, Charli XCX, Tyler, the Creator, Sam Smith and headliners Metallica. Watch all the action live from Lollapalooza here.