Queen Elizabeth II issues an Order-in-Council, proclaiming the House of Windsor and declaring that her descendants will take the name Mountbatten-Windsor.

Elizabeth II was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until her death. She had been queen regnant of 32 sovereign states during her lifetime and was the monarch of 15 realms at her death. Her reign of 70 years and 214 days is the longest of any British monarch, the second-longest of any sovereign state, and the longest of any queen regnant in history.

An Order in Council is a type of legal instrument issued by the executive branch of a government, often the head of state or their representatives, on the advice of a cabinet or council of ministers. These instruments are used in several Commonwealth realms, with equivalent instruments also found in countries with a Westminster system of government. Although the specifics vary by country, Orders in Council typically allow the executive to make formal decisions or regulations without enacting new legislation.

The House of Windsor is the current reigning house of the United Kingdom and other Commonwealth realms. The house's name was inspired by the historic Windsor Castle estate. The house was founded on 17 July 1917, when King George V changed the name of the royal house from the German Saxe-Coburg and Gotha to the English Windsor due to anti-German sentiment during the First World War. There have been five British monarchs of the House of Windsor: George V, Edward VIII, George VI, Elizabeth II, and Charles III. The children and male-line descendants of Queen Elizabeth II and Prince Philip, Duke of Edinburgh, also genealogically belong to the House of Oldenburg since Philip was by birth a member of the Glücksburg branch of that house.

Mountbatten-Windsor is the surname available to descendants of Queen Elizabeth II and Prince Philip, Duke of Edinburgh and can be used by them whenever a surname is required. Generally, those that are entitled to, and use, the royal style HRH Prince or Princess have no need of a surname. An example of when a surname is needed is when they get married. Mountbatten-Windsor combines the British royal family's House name of Windsor and Prince Philip's adopted surname of Mountbatten. Its use was authorised by a 1960 Privy Council declaration.