Carpool Karaoke has become a huge 21st century cultural phenomenon.

James Corden gets massive celebrities in his car, drives them around, lays the chat on and then they sing some of their greatest anthems. So simple, yet so brilliant. But Corden's Late Late Show concept, which has taken on a life of its own (quite literally as Apple have snapped it up) almost didn't get off the ground. Literally nobody wanted to be on it and it was only by complete luck that they managed to blag Mariah Carey into being the first on. However we're not too sure whether the concept was even explained to her - no matter how simple it was. It transpires that Mariah didn't even realise that she was supposed to sing on Corden's new Carpool Karaoke segment. Late Late Show producer made the revelation at the Edinburgh International TV Festival as he explained ‘every publicist you can think of’ initially refused to let their talent appear on the segment.' Watson, who had to corner one of Mariah's team at a party to get her in Cordern's famous SUV, said: ‘The next day it was booked and we were shooting it. I don’t know what Mariah thought but when James pressed play she was like “We are not going to sing”. You can see how she reacted when Corden slips one of her tracks on the radio - it's either an elaborate hoax or she really was clueless that she really was there to sing along to her own music. Whatever though, she handled it like a pro. That first ever video has clocked up a ridiculous 27 million views on YouTube. It was always going to be a hit, wasn't it? https://youtu.be/z2iwQoKD6mg But the authenticity of the idea clearly struck a chord with the world and Watson explained that it's the simplicity of the segment that has made it such a hit. ‘That is why it works, when people appear on show they usually want to sing their newest stuff, which is the last thing anybody wants to hear, but with carpool we just put their greatest hits in there,’ he said. ‘You can’t normally ask Britney Spears to come on a show and sing …Baby One More Time…It struck a chord, it creates intimacy in such a lovely way. 'There are no publicists or make up artists, just James along with these people singing wonderful music. It’s very joyful and it resonates.’