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.

The “Shallow” singer closed out the star-studded benefit concert with a song she co-wrote for the show with her fiancé, Michael Polansky.

Mikael Wood and August Brown are at Inglewood's Intuit Dome and Kia Forum for the FireAid benefit concerts starring Billie Eilish, Lady Gaga, Green Day and Stevie Wonder, among many others.

Lady Gaga closed the FireAid concert in Los Angeles with a live performance of her hit "Shallow" and a brand new song written for the occasion.

After almost six hours of FireAid, Lady Gaga ended the historic Los Angeles event by debuting a new song co-written with her fiance Michael Polansky, an upbeat number that she said was “just for tonight.”

Lady Gaga is ramping up to the release of new album Mayhem, and she’s popping up all over the place, from December’s A Carpool Karaoke Christmas to next month’s SNL 50th anniversary concert. Also on her schedule as FireAid,

Sting, Billie Eilish, Rod Stewart, Stevie Wonder and Lady Gaga are among the stars performing at a huge benefit concert in Los Angeles to help the area recover from recent devastating wildfires.

The concert will also be screened live at select AMC Theatres and and Regal Cinema locations in the U.S. If you will be on the move, iHeartRadio, the national audio partner for the event, will also feature the FireAid concert across over 860 radio stations in the U.S., digital platforms, and the iHeartRadio app.

FireAid, a star-studded benefit concert raised millions for LA wildfire victims. The event featured emotional performances, including a surprise Nirvana reunion, Lady Gaga debuting a new song, and Billy Crystal hosting with humor.