Billie Eilish gave "Barbie" heart with her somber soundtrack tune, and now she's opening up about the dark inspiration behind it.

The "What Was I Made For?" singer reflected on the pensive ballad she wrote for Greta Gerwig's existential comedy in an interview with the Los Angeles Times published Tuesday.

Eilish, who broke out with the success of her 2019 debut album "When We All Fall Asleep, Where Do We Go?", said the song's lyrics were inspired by her changing relationship with fame and how she'd been "basing all my happiness on all these things in the material world that you have no control over and that will inevitably change."

"I felt like I was on the moon (in 2019). And I remember at the time being like, I'm finally happy. I'd never been happy before, and I just wanted to stay happy," Eilish told the outlet. "I got older and fell back into being a human and not being happy all the time — having good moments and having bad moments. Last year got really bad. And I just kept being like, 'God, I miss 2019 so much. When can my life feel like that again?' "

Eilish said an inspiration for her in understanding the loneliness that comes with fame is singer-songwriter Kurt Cobain, the late frontman of Nirvana who died by suicide in 1994.

"I feel so much deep, deep, deep sorrow for him and his life and where it went. In (his suicide) letter he's like, 'I have everything in the world, and I absolutely hate it.' He was so ashamed that he wasn't enjoying it," Eilish said. "And I get why he was feeling that way. It's just not what you think it’s going to be."

Billie Eilish on feeling 'very protective' of Olivia Rodrigo

In her conversation with the LA Times, Eilish also spoke about looking out for the next generation of young women, including fellow popstar Olivia Rodrigo. The "Bad Guy" songstress revealed that Rodrigo – who found teen stardom with her debut single "Driver’s License" – was a muse for her song "Goldwing," taken from 2021's "Happier Than Ever."

The song's lyrics describe a "gold-winged angel" who's in danger of being exploited. "Gonna claim you like a souvenir / Just to sell you in a year," Eilish sings.

"Olivia was getting big, and she was just, like, this little dainty child," Eilish said. "I felt so nervous. I was worried about her. She came up in that acting world, and people are so weird. I don’t know — I just felt very protective over her. And I feel that way to everyone."

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Eilish added that while "everybody's experiences are so individual," she feels a deep kinship with young women in the public eye.

"I just see myself in all these young girls. And it's the girls, man. Boys can handle themselves. They’re dudes — they don’t have to deal with it like we do," Eilish said. "I just want to hold everybody in a little glass box and never let anything touch them."

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Billie Eilish opens up about gender identity, attraction to women

Eilish got candid about her relationship with women in an interview with Variety published Monday.

"I've never really felt like I could relate to girls very well," Eilish told the outlet. "I love them so much. I love them as people. I'm attracted to them as people. I'm attracted to them for real."

The "Lost Cause" singer, who's drawn scrutiny over her sexuality in the past, also alluded to her experience of same-sex attraction. Eilish did not disclose if she identifies as queer, however.

"I have deep connections with women in my life, the friends in my life, the family in my life," Eilish said. "I’m physically attracted to them. But I’m also so intimidated by them and their beauty and their presence."

Although Eilish penned a female empowerment anthem with "What Was I Made For?", the singer spoke about the disconnect she's felt to her womanhood.

"I’ve never felt like a woman, to be honest with you. I’ve never felt desirable. I’ve never felt feminine. I have to convince myself that I’m, like, a pretty girl," Eilish said. "I identify as ‘she/her’ and things like that, but I’ve never really felt like a girl."

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