Billie Eilish and her brother Finneas were both "really inspired" to write a song after seeing scenes from Barbie.

The Bad Guy singer and her songwriting partner were approached by Barbie director Greta Gerwig about writing a song for the movie and they were "blown away" and "really inspired" by the scenes they saw.

"Honestly, it was literally the next day after we saw the movie and we were both just really, really inspired by the film and wrote a song about it," Billie, 21, told The Hollywood Reporter.

Finneas noted that they are both huge fans of Gerwig's films and were keen to check out her take on Barbie.

Eilish added, "I was just really intrigued in general, like before even thinking about making a song, I was like, 'Oh I wanna see! I want to be a part of this!' I was like, 'Maybe we won't make a song but I want to see it! I want to see Margot Robbie... as Barbie, are you kidding me? It's my dream!'"

The Grammy winner then recalled how Gerwig approached them with the idea, saying, "(She) was like, 'I don't know, I just want you guys to do something,' (she) showed us a couple of scenes, a good amount of the movie actually, and then she was like, 'Whatever is inspiring to you, just be inspired... You don't even have to do anything but it would be really cool if you did.'"

The sibling duo ended up writing What Was I Made For? for the movie's soundtrack.

They previously won the Best Original Song Oscar for writing the theme for the 2021 James Bond movie No Time to Die.