Jimmy is talking about Kelly being on the show and he says he can't understand why nobody wants to do a duet with her. "I don't know what they're talking about, I would LOVE to do a duet with Kelly Clarkson," he says...and suddenly, she appears out of nowhere and the duet is ON!
Of course, Jimmy didn't just want to do A DUET with Kelly, he wanted to do a montage of a whole bunch of famous duets. They cover everything from Stevie Nicks and Tom Petty's "Stop Draggin' My Heart Around" to Pink and Nate Ruess' "Just Give Me a Reason" and pretty much everything in between.
To all the people who passed on doing a duet with Kelly: Your loss!