[Fuzz]

Queen Elizabeth was born with the last name Windsor. But that wouldn’t have been the case before 1917, the year her grandfather, King George V, decided to not only switch his house name from Saxe-Coburg-Gotha to Windsor in order to head off anti-German sentiments during WWI, but also designated Windsor as the royal family’s official surname going forward.

Before 1917, British royals went only by their first name and the name of the house or dynasty they belonged to, such as Tudor or Hanover—i.e., Queen Victoria of the House of Hanover.

Following her marriage to Lieutenant Philip Mountbatten—later Prince Philip—in 1947 and her ascension to the throne in 1952, Queen Elizabeth II made a slight adjustment to her grandfather’s naming decree by adding a hyphenated “Mountbatten” to the last name of her descendants to reflect the surname of her husband.

https://time.com/5219397/royal-famil...eth-last-name/

Interesting article on the last name of the Royal Family.