Julia Roberts, George Clooney crash Gwen Stefani's epic Carpool Karaoke

You know what's really "bananas"? Singing "Hollaback Girl" with not just Gwen Stefani, but also George Clooney and Julia Roberts.

That's what James Corden got to do when Stefani took a ride with him for the latest "Carpool Karaoke" on the "Late Late Show." The pop star belted "Don't Speak," talked about her prolific emoji use and schooled the TV host on getting the lyrics right to "The Sweet Escape" -- though Corden had to teach Stefani about the implications of the eggplant emoji.

But later, Corden and Stefani realized they needed two more passengers to use the carpool lane so the late night host could get to work faster -- so he made phone calls to a couple of friends with nothing better to do.

Those friends would be Clooney and Roberts, who hopped into the back seat for a rousing rendition of "Hollaback Girl" and more.

Watch the full video to see if the Oscar-winning actors have a future in the pop industry.