Avril Lavigne is the "motherf---ing princess" of pop-punk, and she proved it with her surprise return to When We Were Young music festival on Saturday.

The singer shocked fans at the Las Vegas event during All Time Low's set when she appeared onstage to sing her new collaboration "Fake as Hell" with the pop-punk band. The crowd went wild as everyone slowly realized it was actually Lavigne onstage and not just a recording of her parts.

After finishing that song, Lavigne and the band — featuring singer/guitarist Alex Gaskarth, guitarist Jack Barakat, bassist Zack Merrick, and drummer Rian Dawson — launched into a rousing version of "Sk8er Boi" in one of the day's highlights as fans of both artists were treated to a rare team-up on the iconic song.

Watch a video of her surprise appearance below:

This wasn't Lavigne's first time performing at the massive emo/pop-punk festival. She was one of the main acts during the inaugural first weekend of 2022's event, but due to "unforeseen circumstances" she said see ya later, boy, and dropped out of the second weekend (Death Cab For Cutie stepped in as a replacement).

While she wasn't officially on the lineup for 2023, Saturday's return cements her status as one of only two artists to play both years (Pierce the Veil is the only artist to be featured on both lineups).

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