The Queen's official title is Elizabeth the Second, by the Grace of God, of the United Kingdom of Great Britain and Northern Ireland.
However, her rarely used surname is Windsor, which was adopted by her grandfather King George V in 1917.
Previously, the British royal family's last name had been Saxe-Coburg-Gotha, which was formed when Queen Victoria wed the German Prince Albert from the house of Sachsen-Coburg und Gotha in 1840.
That surname was changed to Windsor by King George V owing to anti-German sentiment during the First World War. He took the new name from his castle.
The Queen, who had been christened Elizabeth Alexandra Mary of York upon her birth in 1926, reinforced Windsor as the royal name in a declaration after she ascended the throne in 1952.
She brought about a slight change eight years later, though, with a declaration that all her children by the Duke of Edinburgh would take the surname Mountbatten-Windsor - apart for those in line for the throne, who would remain Windsor like her.
Mountbatten had been the Anglicised name adopted by Prince Philip, whose mother had been Alice of Battenburg, upon his marriage to Queen Elizabeth II in 1947.