"In my head," 4-year-old Sydney Keiser said.

Sydney began designing outfits when she was 3 years old, after her mom, Angie Keiser, had her make a construction paper dress as an arts-and-crafts project.

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Angie showcases her daughter's designs, which are all made out of paper, on her Instagram account. More than 448,000 follow the account, all wanting to see what Sydney will dream up next.

Angie almost didn't believe it when J.Crew's executive creative director, Jenna Lyons, emailed her earlier this year expressing interest in working with Sydney.

"I remember reading the email and being certain it was a set up. As in, it's probably some kind of wicked virus that if I reply to it, my laptop will explode or at the very least melt before my eyes," she wrote on her blog, Fashion by Mayhem. Mayhem is Sydney's nickname.

Despite the hesitation, Sydney and her family flew to New York to meet with Lyons. J.Crew officially announced the collaboration last week on social media, writing, "The designer of our next #crewcuts collaboration? 4-year-old fashion blogger and paper dress maker, Mayhem."

The clothing company wrote on its blog that it's been busy transforming Sydney's paper creations into a wearable kids line.

Working with Sydney is a departure for the brand, which up until now has joined forces with some pretty big name designers.

This past fall, J.Crew teamed up with Joseph Altuzarra for a limited seven-piece collection. If his name sounds familiar, it's because he recently collaborated with Target, as well.

It's also currently working with high-end British shoe designer Sophia Webster.

Sydney's children's collection will hit stores next summer. To get the inside scoop on the girl who's likely the world's youngest fashion designer, head on over to J.Crew's website.