The legendary rocker unexpectedly took to the stage with band Borderline Toxic to play Green Day’s Basketcase at Slim Jim’s Liquor Store.
The footage showed Billie Joe joining the band and launching into the hit song from the band’s album Dookie, while Borderline Toxic’s Kerry Glass eventually joined in.
Speaking to the BBC, Ms Glass said: “Eleven-year-old me panicked. I think I did three circles just running around the stage until he was like, ‘Come on, sing with me’.”
She said that her idol joining her on stage was a big moment as Green Day was one of the first bands that got her interested in the genre.
“I used to sit in my bedroom and listen to all their albums. So I’ve got zero chill over this. This is amazing,” she said.
So when one of her idols got on stage with her it was a big moment.
“Honestly, I started getting a bit overwhelmed. I had to just put my phone behind the bar and I was like, ‘I just want to enjoy this moment. I don’t want to look at it. I’ll deal with it tomorrow.’
“I got about three hours’ sleep.”
It was not clear why US singer Armstrong was in Islington at the time.
Since footage of the clip was shared by the band on social media, Ms Glass said her phone had been ringing constantly.
She added that the footage had led to old acquaintances getting in touch to share their reaction to seeing her sing with the rock legend.
Borderline Toxic describe their music as alt-rock with “funky, face-melty riffs and lyrical twists”.