Prince William’s birth certificate shows that his name and surname is His Royal Highness Prince William Arthur Philip Louis. So he does not have the Mountbatten-Windsor surname on his birth certificate.
Prince William Surname: Mountbatten-Windsor Wills was born Prince William Arthur Philip Louis Windsor on 21 June 1982, and his official title was His Royal Highness Prince William of Wales. The name Wales comes from the area over which his father holds title. Following his marriage to Kate Middleton in 2011, he became the Duke of Cambridge, Earl of Strathearn and Baron Carrickfergus. During his military service, William used the name Wales, known as Captain William Wales.
The royal baby‘s surname is unclear at this point, but it could be Mountbatten-Windsor. Prince William and Duchess Catherine typically don’t use the surname, because of the titles before their first names. George V in 1917 declared that Windsor …
Queen and senior royals arrive for annual Order of the Thistle service