Greg is absolutely starstruck when Elmo drops by the Radio 1 studio. After gushing about meeting Katy Perry, Ricky Gervais, and Tom Cruise, Greg declares Elmo his favorite guest ever—then immediately gets caught out when Elmo calls him out for saying the same thing to everyone. Things get chaotic when they attempt an impromptu karaoke duet of Cee Lo Green's 'Forget You' and Katy Perry's 'Firework', with hilariously off-key results and Elmo struggling with the lyrics.