Zelda's Last name is Hyrule right? The king in WW says his full name and Hyrule is the last one. Zelda Hyrule.
Honestly, I don’t think it’s ever explicitly stated? I know that in the old cartoon her last name, as well as the king’s, is Harkinian. But I’m not sure about the games so Hyrule seems like a good guess to me!
If you want to get really technical about it though, I think some royal families don’t even have last names at all. I’m not entirely sure though, but I don’t even think the royal family of England have last names. I remember trying to look it up when the royal wedding was happening and I got really confused by how it worked (I was also much younger lol) so maybe that’s a possibility too?