Prince Williams' family name is Mountbatten-Windsor however the Royal Family don't tend to use surnames unless the situation requires it, in which case, the surname will be allocated depending on the person's title and status.
Depending on the situation, the surnames 'Wales' or 'Cambridge' could also be (and have been) used by the Prince
Queen Elizabeth runs the Royal House of Windsor, and Windsor is the family's (including Prince William's) last name.
Hayley was born Hayley Nichole Williams, so Williams is her real surname.
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Prince William's real name is william arthur philip louis
His full name is Prince Rogers Nelson.
His real name is Prince Rogers Nelson
Queen Elizabeth runs the Royal House of Windsor, and Windsor is the family's (including Prince William's) last name.
His real name is Prince Rogers Nelson
The Prince of Persia's real name, it is Trevor Holloway.
His real name is Prince Rogers Nelson
Prince Michael's real name is Michael Joseph Jackson Jr.
The rapper Birdman's real name is Bryan Williams.
His real name is actually Sonny bill Williams and his name comes from Samoa.