In a special statement for television, the Prince of Wales said the Queen Mother had served the nation with style and dignity for nearly 80 years.
"Her houses were always filled with an atmosphere of fun, laughter and affection."
He added tearfully: "She was quite simply the most magical grandmother you could possibly have."
Earlier on Monday, special gun salutes were fired around the country, to start nine days of official public mourning.
Flags have been flying at half-mast around the UK, and sporting and racing events have been holding a minute's silence.
Thousands of people have signed books of condolences, and left flowers at various sites around the country.
Coffin
It will be brought to London for the funeral at Westminster Abbey on Tuesday 9 April.
It won't be a day off school - but many schools will try to arrange lessons so you can see the funeral if you want.
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