Jan. 7, Billie Joe Armstrong watched Callum McMorran perform Green Day's 1997 hit "Good Riddance (Time of Your Life)" at a Liverpool club.

Imagine belting out a cover of a song - only to be joined by the lead singer of the original ... They were performing Basket Case by Green Day in a London pub when the band's frontman Billie ...

While McMorran played the 1997 classic on acoustic guitar, footage from the venue showed that Green Day's lead singer was also filming the performance on his phone in an Instagram post.