Billie Joe Armstrong just made a Green Day fan's dream come true.

A now-viral video shows Armstrong as he surprises a Green Day cover band, Borderline Toxic, in London and plays a classic song with them, leading fans to praise the singer over his heartfelt move.

Billie Joe Armstrong Joins Green Day Cover Band on Stage

Green Day's official Instagram page posted a new reel sharing a copy of the video of the band's vocalist when he performed on a stage in a London bar. The 51-year-old crooner also took over the mic and sang "Basket Case," a hit song released in 1994.

"When you walk into a pub and the cover band starts playing your song," the caption reads.

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After the moment, Borderline Toxic expressed the bandmates' pure joy after getting the chance to play with the Rock and Roll Hall of Famer. It said that the vocalist, Kerry Glass, was glad to be able to sing with her childhood idol.

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  Armstrong will hype fans in the next few months as he has scheduled gigs in the US. He also celebrated the 25th anniversary of Green Day's album, "Nimrod," by sharing a special re-release that features 14 unreleased demos and live material.

Why Billie Joe Armstrong Does Not Want To Call Green Day a Punk Band

Decades after Green Day's debut, the band remains of the best groups in the music industry. However, the frontman clarified that the band should not be labeled as punk.

In a past interview (via Rock Celebrities), he shared how the band's popularity and its genre caused them to witness Green Day's category transcend to punk. However, he reiterated that the group was no longer part of a small, underground community.

"It's become mainstream. It's no longer an alternative. I think that's one of the big things that people get wrong. We don't go around and wave punk-rock flags, and we never have," he said. "We were definitely influenced by the late '80s hardcore scene, but we don't really live for it."

Green Day proved several times that the group was no longer an underdog compared to its early days following its 1987 debut.

The rock band already released several hit albums, including "39/Smooth," "Insomniac," "Warning," "21st Century Breakdown," and "Revolution Radio."

It also brought home nearly a hundred recognitions from different accolades like the American Music Awards, Billboard Music Awards, and ECHO Awards, to name a few.

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