I looked it up, and some people suggested that the wanderer was originally supposed to be Leoric's son? Maybe he still is - maybe the Prince was his (or her) brother or something. He came back from a long journey to find his father dead and his brother possessed. It would make sense if the hero from Diablo 3 turns out to be the son of the wanderer and Adria - Diablo may have a tie with that bloodline from some pact that Leoric made - maybe the one that cursed him.
I don't know, probably not. But it'd be a fun twist.