British King, George V, declares that he and all his descendants would be going by Windsor. Both in a “House of Windsor” capacity and as an official last name. Before George V picked Windsor, the royals were going by the “House of Saxe-Coburg and Gotha.”
The change came about because of the strong anti-German sentiment following World War I. In 1960, Queen Elizabeth II and her husband Prince Philip announced the creation of a brand-new last name for their untitled descendants which honored both their families: Mountbatten-Windsor. But did not change the name of the House, which is still the House of Windsor.