Los Angeles, Jul 14 (IANS): Singer Billie Eilish loved playing with her Barbies to express her personality.

The 21-year-old pop star has penned and released the track 'What Was I Made For?' with her brother Finneas for the soundtrack of Greta Gerwig's summer film 'Barbie' and explained that playing with the iconic Mattel doll was a huge part of her childhood and thinks that the character is a way of representing everyone, reports aceshowbiz.com.

"Oh gosh. Well, Barbie was my childhood. Truly, Barbie was my every day as a kid. It's a beautiful doll, please. She's everything, too. She's everyone. There's so many Barbies and there's so many different versions and different... all my Barbies had their own personalities and opinions and thoughts, and styles and ideas of the world. And I was just a little kid talking for them, but they still had the personality to me," she said to Zane Lowe on Apple Music 1.

The 'Happier Than Ever' hitmaker went on to add that she has had to keep her part in the "Barbie" movie a "secret" for so long and that her involvement in the summer comedy - which stars Margot Robbie in the title role and Ryan Gosling as Ken - came about after a casual phone call with director Greta and composer Mark Ronson.

She said, "God, it's so funny that it's all out now or coming out now because it's been such a secret for so long. At some point at the end of last year, Finneas was like, 'Dude, would you want to make a song for Barbie?' And I was like, 'What?' I was like, 'Where did you get that question? Why did that come into your brain?' "

"And he was like, 'Well, I was talking to so-and-so, and it came up. And talking to Mark and Greta,' and da, da da. And he's like... there's some random day in December Finneas goes, 'We're going to ...' No, no, no, I get a text. It's like a group text and it's me, Finneas, and then two other numbers. And suddenly Finneas is like, 'Hey, this is Billie's number.' "

"And I look, and I'm like, I don't know what the hell is going on. There's no pre, I don't know what's going on. And then it's like, 'Hey, this is Greta. Hey, this is Mark.' And I'm like, oh, okay. So then they basically send a couple, I don't know, they explain stuff. Greta explains some things about the movie."

"I had heard of it when the internet heard of it like a year ago, and they were shooting and everyone was like, oh my God, it's Margot Robbie and it's Ryan Gosling, and it's all this stuff. Anyway, Finneas goes at one point, Finneas is like, 'At 3:00 PM today, we're going to call Greta and Mark.' And I'm like, 'Cool.' No team, no anything else. That was it."

"And we got on a call with them. Greta explained to us the movie, and it was just the sweetest, most pure thing in the world. And of course, Finneas and I went into this honestly in a very selfish way of, we totally might not have anything to do with this movie, but I want to see it. Show me. I want to see it."