So from what I can gather here, we're looking at MacFinn's bastard son that he had with Tera West (from the "cursed" emphasis-MacFinn, and the eyes-Tera). Tera knew how to keep MacFinn away from people when he went all Loupy, so that would explain why there have been no Loup Garou sightings since MacFinn died. I don't think we know enough about how the family curse works to determine if Fitz starting getting all Loup at the next full moon after MacFinn died, or if its age-related, or if there's some sort of time break before the curse kicks back in again. Its possible that Fitz hasn't started changing, but will at any time now. Its also possible that he has been changing for a while now, but wasn't with Baldy long enough to have gone through a full moon cycle.
Some other conjections: If my guess that Tera was his mother is correct, it could be that her wolf nature ameliorates the Loup Garou change somewhat. If the curse was to become what a human would term "a ravening beast", the Loup Garou would result from a human transforming. To a wolf, which Tera was - even though she could shape change to a human, "a ravening beast" might mean something completely different. Heck, to a wolf, it might mean a human hunter, so the Loup Garou transformation may not result in a full-on "American Werewolf in London" thing, but rather something that looks more like Hugh Jackman in the Wolverine role, which would make him easier to pass as human and not quite so bloodthirsty.
The royal bastard link would make him a prime candidate for Michael's sword, eventually - possibly even setting up a big showdown of Fitz vs Daniel as Daniel strikes me as the type to feel that his father's sword is somehow his birthright.