Billie Eilish's "body problems" began when she was just 10 years old

She told Complex magazine: "What's really interesting is that when I was a little girl, I loved big dresses. All I wore was fairy dresses and skirts. I never wore pants or shorts when I was a little kid. But when I got to be about 11, I got obsessed with this brand called Brandy Melville. And they only sold clothes in one size.

"I was chubbier and I was obsessed with these clothes, but I'd buy a shirt and it wouldn't fit me. That's when my body problems started.

"I was around the age of 10 or 11. I got boobs at like nine, and I was just developing really early. I wasn't slim. Also, I was in ballet, and that's this whole world of body problems.

"I was wearing all these baggy clothes, and it was my style, but at the same time, it was how I could feel comfortable in my body and not feel tied to how my body looks. I didn't want my body to be part of my outfit. I wanted my outfit to be my outfit, and my body happens to be inside it."

The 'What Was I Made For?' singer began changing up her look around the release of her 2021 album 'Happier Than Ever' after growing tired of how she was perceived and embraced an "extreme" image of a "girly girl" in order to defy expectations.

She said: "Then [my career] got to be big, and when I was around 16, I was put in such a box of, like, 'Billie Eilish wears baggy clothes only. And she's not a woman. And she doesn't look like a girl. And she's not desirable.'

"So when I made 'Happier Than Ever', I was kind of like, 'OK, people have decided that I'm this one thing. And I am that thing. But I'm also all these other things.'

"So of course, classic me, I had to go with the completely extreme version of it. I couldn't just, like, wear a skirt once. I had to completely reverse everything and be this girly girl for a second and have these pink nails, blonde hair, skirts, dresses, button-ups, bras, and lingerie. I really just did it to prove a point. I was just like, 'F*** you guys. I can do whatever I want. And then I can go back to what I was doing before, and you guys can eat it.' "

And Billie doesn't regret her temporary image change as she feels she is now "freed from the box".

She added: " So even though it was a little extreme how I did it all, I feel really grateful for it...

"What's great is, once I did that, it was like, 'Now I'm free and I can do anything that I want. And that box is gone.'

"Whether or not other people felt like this, I feel like I freed myself from the box."