Billie Eilish on Which Barbie She Would Be and Upcoming 'Barbie' Soundtrack Song (Exclusive)

Eilish has a song on the highly anticipated soundtrack for the film, out July 21.

When it comes to being a part of Barbie Land, Billie Eilish and Finneas were in right away.

ET's Will Marfuggi spoke to the pair at the Barbie world premiere in Hollywood Sunday, where they spoke about their track, "What Was I Made For," which is featured on the highly anticipated film's upcoming soundtrack.

"When we heard about it, I was like, 'Well, yeah.' And then it was like, obviously you gotta see what you're working with and then go from there. But I was pretty in, I think we were both pretty in right away," Eilish shared. "And then as soon as we saw a couple clips of it, it was over. It was like, 'Okay, we're doing this.'"

Finneas added, "It's so touching, and it made me really emotional. I think sometimes, you look at something from an objective standpoint of, 'People are going to love this.' And then when it becomes personal and it becomes like, 'Oh no, I love this authentically,' that's when we look to like be involved in something like that."

"It's incredible," Eilish gushed.

In terms of the songwriting, Finneas said that the track was very much inspired by the film, with the GRAMMY-winning songwriter noting that they wouldn't have been able to pen the track without seeing at least some of the film first.

"I think in terms of writing a song for it, we like everything to be bespoke, so you know, we couldn't write a song that we felt was worthy until we've actually seen it, and we were writing something that was really inspired by the movie itself," he explained.

When it comes to really diving inside the world of Barbie and in this case, the many Barbies that make up the Greta Gerwig-directed film, Eilish said identifies most with the Fairytopia Barbies.

"I don't know... I love Holiday Barbie. I love all the Fairytopia Barbies. Mermaidia Barbies. Nori," Eilish said. "I don't know. I love Barbie. I would love to be one."

As for who else is on the star-studded soundtrack, Nicki Minaj and Ice Spice recently dropped their single, "Barbie World," which samples Aqua's hit 1997 song, "Barbie Girl," with Dua Lipa, Karol G, PinkPantheress, and more also contributing to Barbie the Album.

Both the film and soundtrack will be released July 21. 

See more of ET's coverage from the Barbie premiere below.