George Clooney and Julia Roberts crash Gwen Stefani's 'Carpool Karaoke': 'You owe me for this one, man!'

Late Late Show host James Corden has drawn some big names in his wildly popular "Carpool Karaoke" segment, but singer and US Voice coach Gwen Stefani may have one-upped him with some superstar guests of her own.

Under the guise of recruiting fellow car-poolers in order to use a restricted traffic lane, mega-stars George Clooney and Julia Roberts land in the back seat – and belt out a pretty impressive rendition of Gwen's 2006 hit 'Hollaback Girl'. 

What follows is a heated debate about what, exactly, a "Hollaback Girl" is (search us!), a recital of some of their infamous movie lines, and a stirring rendition of Queen's 'We Are The Champions'.

When asked about how she maintains her young appearance, Gwen said it has a lot to do with being in love.

"What happened was my life blew up, and after that I kind of started falling in love," she said, referring to her romance with country singer and fellow Voice coach Blake Shelton.

"That's, like, what the face-lift is, I think!" she joked.

"I'm writing music that's about happiness and truth."

The pair also discussed Gwen's love of emojis and belted out some of her best-known smash hits, including 'Rich Girl' and 'Don't Speak'.

We're guessing our invite was lost in the mail.