The six-year-old, who had the genetic disorder Batten's disease, became known nationally because of his parents' efforts to save his life. Barry and Carmen Daniels, who have adaughter, Charly, aged nine, with the same condition, fought to obtain the best treatment for Daniel, which led them to challenge the previous government in the High Court.
Last September, as the conditions of both children deteriorated, they announced that they would not subject them to further painful treatment and the next time they contracted a serious illness they would be allowed to die. They said they believed Rhys and Charly had suffered enough.
Yesterday, a friend of the family said the paarents were too upset to speak about the loss. "Rhys passed away last night and they are coming to terms with it," she said.
Batten's disease is a metabolic disorder which takes hold at about the age of three and progressively causes blindness, dementia and immobility, and usually kills sufferers by the age of 10. Rhys was diagnosed at two and his parents believed radical treatment might save him. Despite two transplants his condition worsened in the past year till he was blind, confined to a wheelchair and had to be fed through a tube.
Charly, who was diagnosed too late for treatment, is also now blind, unable to use her limbs and can no longer communicate. At the time of their announcement that they had given up the fight to save them, the Daniels signed forms saying that there should be no life support for the children. Speaking at the time, Barry Daniels said: "It was agonising, heartbreaking, dreadful, but we have to do what is best for our kids. It is not a decision we ever wanted to have to make ... But we have decided that when Rhys and Charly next fall ill or get an infection we don't want them being rushed to hospital and having needles and tubes stuck in them. We don't want them to be resuscitated. We want them here at home where we can soak them up in our love and let them die peacefully."
Rhys became the first child in the world to have a bone marrow transplant for Batten's disease after his father spent months persuading doctors to carry it out. Then Westminster Children's Hospital, where he was being treated, was closed and it took further months of searching to find a hospital prepared to carry out the surgery. The Daniels challenged the government's decision to close the Westminster hospital in the High Court, which concluded that the decision had cost Rhys "valuable, perhaps vital, time". The transplant was finally conducted at the Bristol Royal Hospital for Sick Children. It failed, and so did a second, leaving Rhys prone to infections.
Mr Daniels, who founded a charity to raise money for sufferers of the disease for which he now works full time, said he had never regretted the treatment Rhys had endured because it might have worked. "You don't know until you try it," he said. The couple has a second daughter, Bliss, almost two, who does not have the disease.