Gwen Stefani did 'Carpool Karaoke,' and George Clooney and Julia Roberts showed up

James Corden's "Carpool Karaoke" segment on his late-night show has seen its share of famous guests, but this is a new level.

Gwen Stefani joined the host in the car to sing some of her songs old and new, from "Don't Speak" to her new single "Used to Love You." (Somehow Stefani makes singing along to herself seem sweet and not narcissistic.)

But then things took a turn when Corden said he had a couple other people joining. Turns out they were George Clooney and Julia Roberts, hanging out in the backseat. And watching Clooney sing "Hollaback Girl" is as funny as you'd imagine. (Stefani also dishes some backstory about the hit.)

And then they all join in on some Queen, as one does in karaoke.

"He sings so good," Stefani says about Corden, seeming genuinely surprised. They're all friends here.

Watch the celebrity jamming below: