The British royal family have run into the same problem. Traditionally, they use a first name and a title, e.g. "Prince William, Duke of Cambridge". For legal p

The British royal family have run into the same problem. Traditionally, they use a first name and a title, e.g. "Prince William, Duke of Cambridge". For legal purposes, they occasionally use the surname "Windsor" or "Mountbatten-Windsor". This is applied rather inconsistently - Prince William enlisted in the Air Force as "William Wales". https://www.royal.uk/royal-family-name https://www.royal.uk/royal-family-name