“Knowing that we have the capability to ... make them feel good about themselves… I just wanted to make her birthday dreams come true,” designer Michael Costello tells PEOPLE

By Rachel DeSantis
December 19, 2019 04:38 PM

Michael Costello has dressed everyone from Jennifer Lopez to Beyoncé, but the designer’s biggest fan just might be 13-year-old Adalia Rose.

Adalia is a typical teenager who loves all things fashion — but she also suffers from progeria, a rare genetic condition that gives her a smaller frame and makes dressing in her preferred styles more of a challenge.

Enter Costello, who recently surprised Adalia with a pair of custom-made dresses for her 13th birthday party in an adorable Instagram video that has since gone viral.

In the clip, Adalia unwraps the gift from Costello, 36, and says “Oh my god,” before giving her mom a knowing look and immediately telling her, “This is Michael Costello.”

“I’m having a moment,” the excited teen says as she proudly dons the dress, a turquoise two-piece inspired by Princess Jasmine from Aladdin.

An additional video features Adalia showing off her dance moves in the dress and happily rocking a second, fuchsia-colored one-shoulder gown that also came courtesy of Costello.

“They are so perfect and I even want to wear them while I’m just at home!” Adalia wrote in the Instagram caption of a post showing her opening the present. “Michael Costello you did such an amazing job making everything I wish you can make all my clothes! I love you so so so much and I send you a million hugs.”

Costello tells PEOPLE that Adalia — a social media star with more than 13 million Facebook followers and nearly 2.5 million YouTube subscribers — has long been a fan of his, and that the pair first met up several months ago in Austin, Texas, after she heard he was in town and reached out to grab dinner.

“It was the cutest. She was so adorable and so sweet,” he says of their initial meeting. “She’s so tiny that you instantly think she’s going to be like a baby, and you want to baby her. But I didn’t realize that she’s 13 years old, and she’s like any other savvy 13 year old. She was a little sassy!”

Michael Costello
Adalia Rose
| Credit: Michael Costello/Instagram

Adalia’s condition, progeria, is characterized by the appearance of accelerated aging in children, according to the Progeria Research Foundation. Symptoms include a lack of growth, loss of body fat and hair, stiff joints and hip dislocation.

Throughout their dinner, the pair chatted fashion, and Adalia explained to Costello — who recently designed the pale pink gown that Jennifer Lopez wore on the cover of PEOPLE’s People of the Year issue — what types of styles she preferred.

Jennifer Lopez wearing a Michael Costello design
| Credit: Miller Mobley

“She said she loves J. Lo, and anything that J. Lo wears she likes to wear, and she loves flowy fabrics and sparkles,” he says with a laugh. “And I said, ‘Okay, you’re my ideal client. You are the Michael Costello girl.’”

Michael Costello
Adalia Rose
| Credit: Michael Costello/Instagram

When the Project Runway alum learned that Adalia would soon be celebrating her 13th birthday, he knew that creating her a pair of custom-made gowns would be the ultimate gift, and worked with the girl and her mother to craft the perfect look, taking special measurements to get the fit just right.

“She knew instantly that she wanted a Princess Jasmine dress,” he says, adding that while she knew that one was coming, the second pink dress was a surprise.

Michael Costello
| Credit: Bryan Bedder/Getty Images for VH1

Though Costello’s resumé is filled with A-list stars who have proudly worn his creations on runways and red carpets, he tells PEOPLE it’s all the more rewarding to dress people like Adalia, whose unique size tends to make it difficult to find clothes that match her jumbo-sized, colorful personality.

“Knowing that we have the capability to make something for them and to celebrate them and to make them feel good about themselves… I just wanted to make her birthday dreams come true,” he says. “I feel like I’ve dressed everyone. It’s an incredible milestone for my career. I feel like I’ve done so much and I’ve been blessed so much, and now what I really want to do is start meeting more people like Adalia… What’s it to me? A couple of days on the sewing machine? A few hundred dollars’ worth of fabric and time, just to make someone else’s dream come true.”