Photo of Kendrick Lamar at Bonnaroo 2015, by Dan DeSlover

Earth, Wind & Fire brought some unexpected guests—not even they knew!—on stage Friday night during their set at Bonnaroo.

Although unplanned, bassist Verdine White spotted Kendrick Lamar and Chance the Rapper to the side of the stage watching and invited the pair to join them for a freestyle.

Lamar had just finished his own set at the fest and neither rappers had ever met the iconic group.

Watch fan footage below (via Fake Shore Drive).