only took off the way it did because Mariah Carey couldn't resist James Corden's boyish charm.
Carey was the first celebrity guest to participate in the Late Late Show segment which launched Corden to international fame, but she was totally unwilling - at first.
Speaking on SiriusXM, Corden talked about kick-starting the segment and recalled a time where he couldn't even book "fifth rate" artists.
"If you imagine an artist, just think of any artist in the world, they said no to it. I mean, everyone ... I'm talking, like, who's the dudes who did Cotton Eye Joe? We were in those sorts of territories," Corden said.
Then, somehow, Corden managed to win over a woman from Carey's record label, who then pitched the idea to Carey, who only agreed so she could promote her Las Vegas residency, and only if she wouldn't be singing.
"She came out and said, 'Oh, I'm not singing today,' and she went, 'We'll just drive around and have a chat,'" Corden said.
"I went, 'Oh, right. It's just, we call it Carpool Karaoke, so without that ...' And then I thought, I've just got to go. I've just got to jump into it.
"Even if this bit is just me singing to Mariah Carey, it's still on the show. It may not be the recurring bit that we hope it is, but it's still probably on the show."
If you watch the Carpool Karaoke episode now, it's clear Carey is hesitant, she even flat out says: "I'm not singing today, I was up all night".
But once Corden turns on the radio and starts singing, Carey can't help but sing along to her hits, caving in when Corden keeps repeating "give me some sugar".
Now, after just a matter of months, Carpool Karaoke has become an online sensation.
Because Mariah Carey gave it a shot and Corden managed to get her to sing along, he's since booked a slew of superstars including Justin Bieber, Adele, Jennifer Lopez, Elton John, Sia, and even actors Julia Roberts and George Clooney.
Corden teased on Instagram that Selena Gomez would be the next celebrity to take part in Carpool Karaoke.