Mountbatten-Windsor
Updated: Wikipedia source
Mountbatten-Windsor is the family surname available to and used by descendants of Queen Elizabeth II and Prince Philip, Duke of Edinburgh, when a surname is required. Generally, those who are entitled to, and use, the royal style HRH Prince or Princess have no need of a surname. A surname may become needed, for example to register a marriage, and for non-royal children. Mountbatten-Windsor combines the British royal family's house name of Windsor and Prince Philip's adopted surname of Mountbatten. Its use was authorised in a declaration by the Privy Council in 1960.