As the oldest head of state in history and the monarch with the longest reign in British history, Queen Elizabeth II.
Charles, the former Prince of Wales, the eldest son and heir of the Queen, has succeeded her as King of the United Kingdom and 14 Commonwealth states.
No official details have been released about what will happen over the coming days, but it is anticipated that the Queen will be given a full state funeral, as is traditional to mark the death of a monarch.
It is also expected that her body will lie in state to allow the public to pay tribute.
The King will sign off the final plans in the coming days.