R&B icon R. Kelly thrilled fans at the Lollapalooza festival in Chicago, Illinois this weekend (02-03Aug14) by joining Chance the Rapper onstage for a surprise performance.

The young hip-hop star helped to close the annual three-day bash on Sunday (03Aug14) by performing before the night's headliners Kings of Leon, and he made sure his set went out with a bang by introducing his fellow Chicago native, Kelly, to the stage, much to the crowd's shock.

During his appearance, Kelly performed The World's Greatest, Bump N' Grind and Ignition (Remix).

The veteran singer wasn't the only unannounced guest during Chance the Rapper's set - he also brought out another local, rapper Vic Mensa, to perform.

Kelly's mini Lollapalooza set took place just days after his headlining show at the Fashion Meets Music Festival in Columbus, Ohio later this month (Aug14) was cancelled following a storm of protest on social media over his controversial past.

The star was indicted in 2002 on charges of making child pornography, but was acquitted in 2008.