The host reveals the song he didn't know before filming and more!

James Corden’s Carpool Karaoke has become a goldmine of viral videos, featuring some of the biggest acts in music singing along to popular tunes in the Late Late Show host’s car. But in an exclusive interview during his Entertainment Weekly cover shoot, Corden reveals how none of it would have been possible without the help of — who else? — Mariah Carey.

“The person that was hardest to convince to do Carpool was basically everyone before Mariah Carey said yes. No one would do it,” he says. “You understand why they’d say no. It’s a weird ask.”

Since its March 2015 debut, the talk show segment has allowed Corden to cruise the streets of Los Angeles while singing with the likes of Iggy Azalea, Stevie Wonder, Justin Bieber, One Direction, Sia, and Adele, whose Carpool Karaoke bit has thus far been viewed almost 90 million times on YouTube.

“The guest who surprised me the most was Stevie Wonder, because we were told very strictly that we only had an hour, and we just shot for two-and-a-half hours because he just kept saying, ‘I’m having a great time, let’s do another one!'” Corden reveals.

Though he has performed professionally himself (he starred in the 2014 musical film Into the Woods and is featured on Kylie Minogue’s 2015 Christmas album), Corden says he still feels anxious prior to filming Carpool Karaoke. “I always get slightly nervous when I’m about to try and harmonize with some of the best singers in the world,” he says, but did admit that he didn’t know the words to Carrie Underwood’s “Jesus, Take the Wheel” before the American Idol winner’s appearance. “That’s why I really want to do one with Sam Smith. I feel like I’ve got some really good harmonies [already] worked out for his songs.”

As for who he’d like to buckle up in the passenger seat for the next karaoke session, Corden leaves the door open to all possibilities. “We’ve got a couple of Carpools lined up which I hope people will like,” he says. “We want everybody to come and do our show, but of course [we’d love to have] Beyonce, Prince, [and] Bruno Mars.”

Watch Corden reflect on some of his favorite Carpool Karaoke moments in the video above.