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

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.

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.”

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.

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.

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,