Ivan Cameron, the six-year-old son of the Conservative party leader, has died.
In a statement the party said:
“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 another son, Arthur, 3, and a five-year-old daughter Nancy.
Prime Minister’s Questions has been cancelled this afternoon as a mark of respect.
Gordon Brown said he and his wife Sarah have sent their condolences to the Camerons.
“The death of a child is a loss no parent should have to bear,” Mr and Mrs Brown said in a statement.
“I know Ivan was a child who brought joy to all those who knew him and his was a life surrounded by love.
“The thoughts and prayers of the whole country are with David, Samantha and their family.”
Tory blogger Iain Dale said that reaction across the political divide was one of shock and sympathy.
“I have read a lot of the reaction on blogs and Twitter and it’s so heartwarming to see the kindness being expressed and the apparent empathy with the Camerons,” he wrote.
“Nothing can prepare you for losing a child. Nothing. I hope David and Samantha take all the time they need before returning to the fray. Their family comes first.”
Mr Cameron, who has been Leader of the Opposition since December 2005, is expected to take some time away from politics. Shadow Foreign Secretary William Hague will fill in for him.
Mayor of London Boris Johnson, a personal friend of Mr Cameron’s said:
“I was shocked at the terrible news this morning of the death of Ivan Cameron. My deepest sympathies are with David, Samantha, Nancy and Arthur.”