Hayley Okines and her family had campaigned to raise awareness of her condition
A girl with a rare genetic condition which made her body age eight times faster than normal has died at the age of 17.
Hayley Okines, from Bexhill, East Sussex, became known as the 100-year-old teenager through her efforts to raise awareness of progeria.
Her mother, Kerry, announced Hayley's death on Thursday evening.
"My baby has gone somewhere better. She took her last breath in my arms at 9.39pm," she wrote.
Her father Mark said Hayley was being treated for pneumonia, and had briefly returned home from hospital on the day she died.
"She came home for an hour and she saw her puppies, little brother Louie and her sister Ruby," he said.
"I think she wanted to come home to say goodbye to everybody.
"I think she knew that yesterday was going to be the time."
Hayley, who published an autobiography at the age of 14, had made a number of appearances where she spoke about her condition.
The teenager had been told she would not live past the age of 13, but she went on to undergo a pioneering drug treatment in the US.
Hayley became known as the "100-year-old teenager"
Hutchinson-Gilford Progeria Syndrome causes accelerated ageing in those affected.
People with the condition also suffer heart problems, lack of growth and loss of body fat and hair.
It affects just 124 children worldwide.
The Progeria Research Foundation posted on its Facebook page: "The entire Progeria family mourns together with many as we say goodbye to Hayley Okines, our smart, beautiful and spirited English rose, who passed away today at age 17."
Phoebe Smith, whose 11-year-old daughter Ashanti also has the condition, said Hayley had inspired a lot of people.
"She will always be loved. She is my inspiration - her and her mum," she said.
"Her memory will definitely live on."