Designer Michael Costello pays tribute to social media star Adalia Rose Williams, who died at 15: 'She was an angel'

• Social media star Adalia Rose Williams died on Wednesday. She was 15.
• The YouTuber had a genetic condition called progeria that is characterized by rapid aging.

Michael Costello, a fashion designer featured on "Project Runway," paid tribute to social media star Adalia Rose Williams after her family announced that the 15-year-old had died.

Costello wrote on Instagram that his heart was "broken" at the news Williams "was called home to God."

"I am at a loss for words and cannot stop crying," he said. "Adalia has been so special to every single person that she met. She was an angel. Despite the cards she was dealt with, she had the most positive attitude and such big dreams of helping everyone around her."

Williams died on Wednesday evening, according to posts on her Instagram and Facebook pages. Her mother Natalia Pallante also posted on the family's shared Instagram page that Williams was "set free from this world" on January 12.

Williams had 2.9 million subscribers on her YouTube channel, where she documented living with a genetic condition called progeria that is characterized by rapid aging. Children with the condition have an average life expectancy of 13 years, according to Mayo Clinic.

Costello added Williams had changed his life, and he would miss her dearly.

"I promise to cherish all the wonderful memories we've had together," he said.

Costello posted four videos with his statement, showing Williams receiving and trying on dresses he had designed and made for her. One of the clips showed a video message from Williams thanking Costello for the dresses.

Costello also shared Williams' family's statement about her death, along with a GoFundMe link to raise money for Williams' funeral costs and medical expenses.