Gwen Stefani's highly anticipated appearance on James Corden's Carpool Karaoke was officially upstaged by some unexpected surprise guests.

Though she and James were having a blast driving around L.A. and singing to some of her big hits both as a solo artist and from her No Doubt days, they quickly realized that in order to get into the HOV Lane they would need two other people to join them in the car.

Thankfully, James knew a guy nearby who had nothing better to do. And George Clooney knew someone else nearby who would love to see Gwen. So Julia Roberts went along for a ride too.

Seriously, no big deal. Just another day in Hollywood right?

Tags: Gwen Stefani Carpool Karaoke