The Queen is now the second-longest reigning British monarch in more than 1000 years.
Queen Elizabeth II acceded to the throne on 6 February 1952 and has now ruled for 59 years and 95 days, more than every other monarch except Queen Victoria.
It puts George III, who was king from 1760 until 1820 during which the United States won independence from Britain, into third place.
The Queen, 85, celebrates her diamond jubilee next year and will become the longest reigning monarch in September 2015.
In April, Prince Charles, 62, broke the record for spending the longest time as heir-to-the-throne.