Billie Eilish surprised her audience when she brought out Hayley Williams during the Coachella Valley Music And Arts Festival in Indio, California, on Saturday.

The 20-year-old musician - who is the youngest headliner in Coachella history - and Williams, 33, gave a rare performance of Paramore’s 2007 hit song Misery Business. 

The Happier Than Ever singer sported an oversized graphic T-shirt and matching biker shorts for the night, and wore her raven tresses in messy pigtails.

The star - born Billie Eilish Pirate Baird O'Connell - paired her casual look with a couple of layered chunky necklaces.

Meanwhile Williams looked cool as ever in a well-fitted black blazer that gave a peek at her trim midsection, and matching black pants.

The Mississippi born beauty wore her auburn tresses in a free-flowing style, rocking bangs that framed her face.

Billie also sported black knee-pads on her knees, which came in handy as TMZ reported that she took a tumble during her performance.

Billie Eilish, one of the major headliners this year, chose to share her stage with some special guests on Weekend 1 and her second appearance on Saturday, April 23 was just as impressive.