Billie Joe Armstrong Surprises Cover Band By Joining Them for Green Day Classic: Watch

The Green Day vocalist darted to a stage at a bar in London this week

Billie Joe Armstrong just gave a Green Day fan the time of her life.

The pop-punk legend, 51, surprised a cover band in London while they were playing Green Day's 1994 smash "Basket Case" during a concert, and the whole thing was documented in a new viral clip.

"When you walk into a pub and the cover band starts playing your song," a post from the official Green Day Instagram account read.

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In the video, the band Borderline Toxic could be seen jamming out to the breakthrough Green Day hit when Armstrong darts up to the stage at Slim Jim's Liquor Store.

If it wasn't clear that it was Armstrong by his bleach-blonde hair, his distinct voice clearly gave it away to the crowd, which went nuts once he started singing along to the Dookie classic.

The band reflected on the fun shortly after the gig, writing on Instagram that the moment they played with the Rock and Roll Hall of Famer was one of "pure joy."

"Thank you Billie Joe Armstrong a million times over for this unforgettable experience 🥹 so glad I got to share this moment with a band I love, in my favorite bar, with all our mates... singing with my childhood idol," Borderline Toxic shared. "What a time 🥹"

Other clips from the moment show Armstrong sharing a mic with the band's lead vocalist, Kerry Glass.

"It's only just sinking in that I used to always wish it was me they'd pick to get up on stage at the live gigs, haha, wishful thinking," she wrote. "Could never imagine the man himself would be getting up on our gig. I honestly couldn't be happier 😢😍"

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Just last June, the Green Day frontman revealed he'd be "renouncing" his citizenship from the United States during a recent concert in London, following the Supreme Court's ruling to overturn Roe v. Wade.

"F--- America. I'm f---ing renouncing my citizenship. I'm f---ing coming here," Armstrong told concertgoers, adding that there was "too much f---ing stupid in the world to go back to that miserable f---ing excuse for a country."

"Oh, I'm not kidding, you're going to get a lot of me in the coming days," the "American Idiot" musician added.

Armstrong does have a few gigs coming up in the States, and recently celebrated the 25th anniversary of the band's album Nimrod in January with a special re-release. The updated LP features 14 unreleased demos and additional unreleased live material.

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