Looking for a fic where Sam becomes a werewolf, but neither of the brothers realized it until Sam started to shift.  I think the fic i remember opened right at the moment the full moon started, so it was right as Sam was starting to change.  This is quite possibly a number of fics, so feel free to rec any that fit or are close to it.  And I'm pretty sure it was wincest.

My second fic search in a week, and I know i read this less than a week ago, i feel kinda sad that I can't find it again.