The ultimate carpool ride! Gwen Stefani's Carpool Karaoke session with James Corden was already amazing before they enlisted the help of their superfamous pals on The Late Late Show — at which point things become totally insane!

Corden and Stefani smashed their way through some of the 46-year-old singer's best hits including "Don't Speak" and "Used to Love You," and the No Doubt singer even gave Corden's wife some tips on avoiding ageing.

"My life blew up, after that I started falling in love and I wrote a whole record about that," Stefani said when Corden asked how it could be that she never looked any older. "That's what the face lift is I think!" she said.

But when the duo came to the HOV4 section of freeway that required four passengers to use the carpool, the Late Late Show segment launched into superstar orbit.

"This guy's got nothing to do," Corden said, as he got George Clooney on the phone.

Clooney, calling Corden a "pain in the ass," then got on the phone to his pal Julia Roberts, and in no time the car was full!

Once his A-list crew were strapped into their seat belts, things got musical.

Watch the clip above to see the entire car rock out to "Hollaback Girl" — not to mention their show-stopping rendition of Queen's "We Are the Champions!"

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