By 1951, George VI's health had deteriorated. The king was not always well and his wife, also named Elizabeth, never forgave her brother-in-law Edward VIII -- whose abdication in 1936 compelled her husband to become king -- for endangering her beloved Bertie's wellbeing.
On February 6, 1952, Princess Elizabeth, then on a tour of Kenya, was told that her father, who she adored, had died.
Elizabeth is also one of the longest-reigning monarchs in British history, ranking behind Queen Victoria (who ruled for 63 years and seven months) and George III (59 years).
If she is still queen on September 9, 2015, she will surpass Victoria as the longest reigning monarch of the British Isles.
Unlike Victoria and George III, who found it difficult to conduct their duties at their advanced age, Elizabeth has made more than 500 public appearances after she turned 80 last year. She has made five State visits, including one to Kampala, Uganda, in October for the Commonwealth summit.
Her reign has seen the British monarchy confronted by one serious challenge after another. It is a testimony to her sense of history and duty, her discipline and focus, that Elizabeth II remains relevant to a majority of the British people even today.
Let us meet up with some other elderly rulers, past and present, and see how they compare with Queen Elizabeth.
Photograph: Chris Jackson/Getty Images
Also read: Remembering Diana