Simon Cowell is missing America's Got Talent's live season 21 finale as he continues recovering from back surgery, NBC confirmed just hours before Tuesday's first finale episode. Stepping into his judging seat for both the September 22 and 23 broadcasts is KSI, the YouTuber and boxer who already judges on Britain's Got Talent.

Cowell has now missed several stretches of the season while recuperating; Kenan Thompson filled in for two September episodes and Heidi Klum covered a three-hour special earlier this month. Producers haven't said when, or if, Cowell will return to the panel before the season wraps.

Fans reacted with a mix of concern for Cowell and enthusiasm for KSI, whose blunt, high-energy judging style on the British version of the franchise has made him a popular pick to fill in stateside.