ROYAL TRIVIA

I was doing a crossword puzzle the other day and this was my clue:
"William and Harry's family name"
I drew a blank. So immediately I began searching my brain for the answer, because I feel like I should know this. I mull it over for 2 days and still I come up with nothing. Im now blaming "baby brain", cuz you know I can use that as an excuse again, when I ask Steve and he has no idea either. He says "Are we both just having a brain fart or what?" Seems like this should be common knowledge. I decide to cheat and look up the answer in the back of the book. When I look up the answer, I went "huh. Im not sure I ever knew that."
So, without cheating or googling, Does anyone know the answer? I will post in a few days.