Ganondork
goo
I think Skyward Sword establishes the Royal Family (Zelda's bloodline) and the castle might be Hyrule Castle. Like how you fight outside Hyrule Castle with Ganondorf in TP. However, I've also heard theories of the falling of a previous Royal Family - before Zelda's family takes control - and that could be their castle. If it's the falling of the previous Royal Family then this will take place in the beginning or middle. If it's the new Royal Family's, then it's gonna happen towards the middle or end.
But of course, we'll just have to find out for ourselves, now won't we?
But of course, we'll just have to find out for ourselves, now won't we?