Finneas O'Connell and Billie Eilish are "best friends"

He said: "Billie has some very strong opinions, not least with visuals. Which is exactly as I want it. I think people superimpose their own relationship with their own family on ours when they think about me and my sister. They say either one of two things: they either go, that's so cool, or they go, I could never do that with my sibling.

"And I totally get that because everyone's relationships are different and very personal. I think more and more the important thing is: we love each other. We are best friends because we're siblings. But separate from that, we just have a really good working relationship. And it's very possible that we could have one and not the other in either direction. We could not like each other as much as people but work really well together, or we could not work very well together but love one another as people. We seem to have both right now. So I'm excited as we go into making the second album - which, thank god we’re doing, as otherwise I’d be in a complete state of panic, especially after Grammys night. Just, you know, the pressure and expectation without having done anything would be too much to take!"

And Finneas hopes his and Billie's sweep at the recent Grammy Awards will inspire other amateur songwriters.

He added to GQ Hype magazine: "Usually at the Grammys, whomever wins you always see this quorum of producers and songwriters all take the stage with the artist. It’s usually about 15 or 20 people and it’s often the same 15 people you’ve seen up there before, all slapping fives, shoulder hugging one another. It's very industry. When we won and were up there I was trying to send a message, I suppose. Those other guys are up there for a reason, don’t get me wrong, they’re incredible. But what Billie and I did is we just stuck to our guns and made this record - on our own. And if you’re a kid out there making your records on your own, in your bedroom, all this is now in the realm of possibility for you too."