Two of the evening top-billed acts, Billie Eilish and Green Day, decided to sneak in an onstage duet. As the band geared up to play their beloved 21st Century Breakdown track “Last Night On Earth,” Eilish shocked viewers by picking up a microphone ahead of her set.

Green Day opened up the benefit concert and were quickly joined by Eilish for a performance of the band’s “Last Night on Earth” from their 2009 album “21st Century Breakdown.” Eilish departed the stage after the duet and Green Day continued with “Still Breathing” and “When I Come Around.”

The all-star FireAid benefit in Los Angeles began with Green Day and Billie Eilish teaming up for the 'American Idiot' deep cut "Last Night on Earth."

Billie Eilish has joined Green Day onstage at the FireAid Benefit Concert. Watch their performance of “Last Night on Earth.”

The FireAid benefit concert will go down in history not only because it features some of the biggest names in music on the same stage, but for the message of hope those artists spread. And, hopefully,