Conservative leader David Cameron and his wife Samantha were tonight mourning the death of their disabled six-year-old son Ivan, comforted by messages of condolence led by the Queen.
Ivan, who suffered from Ohtahara Syndrome, a severe form of cerebral palsy which also involves a rare and severe epilepsy syndrome, was taken ill overnight and died this morning shortly after arriving at St Mary's Hospital in Paddington, London.
His parents were with him when he died.
He was the couple's eldest child and had required round-the-clock care all his life.
A Conservative Party spokesman confirmed the news, saying: "It is with great sadness that David and Samantha Cameron must confirm the death of their six-year-old son Ivan.
"Ivan, who suffered from cerebral palsy and severe epilepsy, was taken ill overnight and died at St Mary's Hospital, Paddington, early this morning.
"David and Samantha would ask that their privacy is respected at this terribly difficult time."
Mr and Mrs Cameron have two other children, Nancy, five, and Arthur, three.
Prime Minister Gordon Brown and his wife Sarah, whose own daughter Jennifer Jane was born prematurely and died just 10 days later in 2002, wrote privately to the Camerons to express their sadness.
Buckingham Palace said the Queen had sent a private message of sympathy.
At Westminster, the Commons was briefly suspended as a mark of respect and Prime Minister's Questions was cancelled.
Instead, Mr Brown told MPs: "I know that the whole House will want to express our sorrow at the sad death this morning of Ivan Cameron at the age of just six years old.
"I know that in an all too brief life, he brought joy to all those around him and I know also that for all the days of his life, he was surrounded by his family's love.
"Every child is precious and irreplaceable and the death of a child is an unbearable sorrow that no parent should ever have to endure.
"Politics can sometimes divide us. But there is a common human bond that unites us in sympathy and compassion at times of trial and in support for each other at times of grief.
"Sarah and I have sent our condolences to David and Samantha and I know the whole country - our thoughts and our prayers - are with David, Samantha and their family today."
Mr Cameron's deputy William Hague, who spoke to the Tory leader before making his statement to MPs, said: "Ivan's six years of life were not easy ones.
"His parents lived with the knowledge for a long time that he could die young but this has made their loss no less heartbreaking."
He added: "Ivan their son suffered much in his short life but he brought joy and love to those around him.
"As David himself has said in the past, for him and Samantha he will always be their beautiful boy."
Mr Brown, whose son Fraser suffers from cystic fibrosis, said earlier in a statement: "The death of a child is a loss no parent should have to bear."
Liberal Democrat leader Nick Clegg, whose wife gave birth to their third son at the weekend, said in a statement: "My heart goes out to David and Samantha at this incredibly difficult time for them and their family."
Ivan was born at Queen Charlotte's Hospital in London on April 8 2002.
He suffered his first seizure within weeks and was in and out of hospitals all of his life.
Ivan was diagnosed with Ohtahara Syndrome - a very rare epilepsy syndrome that occurs in childhood.
Children with the syndrome will have severe cerebral palsy, difficult to control epilepsy and delays to their development.
In Ohtahara Syndrome seizures start before the child is three months old and usually occur in the first 10 days after birth.
Describing how he learnt of his son's illness, Mr Cameron once said: "It hits you like a freight train because all the expectations you have for your child change immediately."
Friends have previously attributed Mr Cameron's modernising leadership of the Conservatives to the NHS care Ivan received.
The illness has also helped the Tory leader realise there is more to life than politics, they have said.
Shadow chancellor George Osborne, a close friend of the Camerons, said Ivan's disability "does not make today's very, very sad and sudden death any less shocking".
"Sadly he has been a very ill boy since the moment he was born, but nevertheless he was always at the centre of family life round at the Camerons," he told Sky News.
"He quite regularly had seizures and problems and would have to go to hospital. He had such a seizure this morning and very sadly died shortly after admission to hospital.
"It has left the Cameron family in a great deal of grief and shock."
Friends said it would be two weeks at least before Mr Cameron would feel able to make public appearances, but stressed he was both enormously grateful for the expressions of sympathy and acutely aware that he was not the only parent who had had to face such a tragedy.Reuse content