Was unable to get back into the studio one day because he forgot his ID card. The security guard would not let him in until James Corden came up with the idea to mimic one of the show's billboards. This happened before the first episode was made.
Not commonly known is that the Carpool Karaoke sketch that became a huge hit on his late show did not actually originate there. Corden attributes the inspiration for this to singer George Michael who on an episode of the UK's "Comic Relief" (2011) joined Corden for an in-car singalong of a medley of Wham! hits like "Baby, I'm You Man". For the debut of Carpool Karaoke on Corden's American Late Late Show, singer Mariah Carey was the first guest to agree to the experience (March 2015).