Dua Lipa fans in San Francisco were treated to an unexpected crossover on Sunday night. 

Midway through a Chase Center concert, the “Levitating” pop star surprised her audience by pulling Green Day frontman Billie Joe Armstrong onstage for a cover of “Wake Me Up When September Ends.”

The duet, which was captured in a fan’s video, begins with Armstrong singing the ballad’s first verse solo, with Lipa joining in on the chorus. In the fan video, audience members can be heard singing along.

Before bringing Armstrong onstage, Lipa explained that she covers local songs at every tour stop: “I thought about San Francisco. I thought about all the incredible music that has come out of it. I thought about one band in particular that would be perfect.”

“And I love this band for so many reasons,” she continued. “I love it because of the rawness, the authenticity the message behind it, the space that it holds for people who feel like sometimes they might not belong. I loved listening to this album in particular when I was little.”

“American Idiot,” the Green Day album with “Wake Me Up When September Ends,” came out in 2004, when Dua Lipa was nine years old.

The English Albanian pop star’s catalog includes the RIAA platinum hits “Physical,” “Future Nostalgia” and “IDGAF.” Sunday’s concert was the second of two back-to-back Dua Lipa shows at the Chase Center, both part of the artist’s Radical Optimism tour. At Saturday’s show, she paid tribute to the City with a cover of “Piece of My Heart,” a track popularized by Janis Joplin.