He says he is "completely devastated" by his grandmother's death.
Prince Charles is on a skiing holiday with Wills and Harry in Switzerland - but is returning to Britain immediately.
She was at the Queen Mother's bedside when she died, and said it was "a very moving and very sad moment, but luckily it was peaceful".
Prime Minister Tony Blair said the Queen Mother had been a symbol of Britain's "decency and courage".
She was "loved and admired by people of all ages and backgrounds," he said.
Former Prime Minister Lady Thatcher said she was "an inspiration during the dark days of war."