Photo of Lauren Mayberry at Treasure Island Festival, by Tim Mosenfelder

Treasure Island Music Festival headliners The National closed out the fest joined by a special guest for their performance of "I Need My Girl."

After performing earlier Sunday at the San Francisco fest, CHVRCHES' Lauren Mayberry appeared alongside Matt Berninger and Co. for a magnetic live rendition of the Trouble Will Find Me standout.

Watch fan footage below.