Kopa23 wrote:Maybe Muffy didn't know that Nala was his child?

Think about it, Nala looks a lot like her mother, so he probably thought it was a rogue's cub or something. As for the 'Simba's lesson' part... Nala would be only related to Mufasa and not Sarabi, so she isn't directly related to royalty if you get what I mean. xD And there's also that tradition of marrying your relatives to keep bloodlines clean or something like that.

(Would explain a lot if Nuka was Scar's son-- sorry, joking)
Well, I'm still more inclined tot believe that Scar is her father when it comes to canon. Because in my own TLK universe, Nala's father is one of my OCs.

I'm sure he'd know,but I'm more sure that he wouldn't cheat on Sarabi,nor be willing to betroth his son with his daughter. Just think about it,it wouldn't make much sense. She does,she actually doesn't look like anyone else in the movie,which is why I'm inclined to think that her father is a rogue.
Actually,in that scene he's talking to Simba as his 'son' not as a part of the royal family so he should have mentioned Nala as well if she was his daughter. But even if she was,she would be connected,she is the king's daughter. And a king can choose his wife and make her queen,even though she isn't royal.
Yes,there is that tradition at some points in history,but I don't think that would apply here,cause it wouldn't fit to Kiara and Kovu being together. Then again,this is a Disney movie,so traditions regarding incest are totally out of the question.
I'd have to agree with you that someone else would be Nala's father,I mean,if you look at the whole TLK universe as a whole,not separated into canon and OC.