Billie Eilish made a surprise appearance on stage with Green Day on Thursday to kick off one of two star-studded concerts in Los Angeles put together to raise funds for people affected by deadly wildfires in California this month.

One of the great challenges faced by the events during Grammy Week, including the FireAid benefit, is how to set the proper tone: How do you have a celebratory event like big concert or awards show without seeming tone-deaf to the tragedy and loss so many suffered in the Los Angeles wildfires that ravaged the

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.

The FireAid benefit was fueled by some of music’s best performers to raise money for Los Angeles-area wildfire relief efforts.

Katy Perry belted out “California Gurls,” and Joni Mitchell offered a rare performance as Angelenos spoke movingly about loss — and resilience.

Billie Eilish and Finneas performed acoustic renditions of "Wildflower," "The Greatest," and "Birds of a Feather" at FireAid.

"From the bottom of our hearts, we love you Los Angeles," Billie Joe Armstrong told the crowd, "and we've got your back no matter what"

Raising money for ongoing wildfire relief efforts in Los Angeles, Green Day and Billie Eilish dueted 'Last Night On Earth' at the FireAid benefit concert.

P!nk, Joni Mitchell, and Lady Gaga were just a few of the highlights in a night that also featured a No Doubt reunion and the surviving Nirvana members

The 67th Grammy Awards will have a bit of a pall over them Sunday after the devastating wildfires in the Los Angeles area.

Billie Joe Armstrong and Billie Eilish. Green Day got things started at the Kia Forum, where they surprised fans with Eilish to help them perform, "Last Night on Earth" from 2009's 21st Century Breakdown.