In the opening to A Link to the Past, as your uncle lay dying, his last words are "Zelda is your..."
He never finishes that sentence, and to my knowledge, there's no official source identifying what he would have said. So how does that sentence end?
Perhaps the most boring possibility is "destiny." Fuck that possibility.
As a Star Wars kid, I always kinda thought it was "sister," which would actually be neat. The whole "surprise family member" thing is a bit cliche now, but it would be a pretty dramatic and surprising shift in the two character's presumed relationship.
Any other possibilities?