Audiences tuning into the FireAid benefit concert for Los Angeles on Thursday night (Jan. 30) were surprised with an early treat when pop superstar Billie Eilish made a surprise appearance alongside Billie Joe Armstrong and the rest of Green Day for a stirring opening performance.

"California, Los Angeles, Altadena, the Palisades - we are in this together," Green Day's frontman Billie Joe Armstrong screamed to a sold-out crowd at L.A.'s Kia Forum on Thursday for the FireAid wildfire benefit concert.

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.