From BuddyTV:

If I took a trip to see sassy psychic Missouri Moseley and asked her what’s coming up in Supernatural’s future, I think I know what she’d tell me: the battle of Winchester vs. Winchester.  Dean has known he might have to face off with his brother since the beginning of season 2, when a dying John warned him that Sam might turn to the dark side one day.  The addition of Castiel to the mythology has only made the brotherly battle more inevitable.  Sam is cranking up his dark mojo with help from a demon, Dean is working for an angel, and the long-dead Yellow-Eyed Demon has a plan for Sam that has yet to be revealed.  None of this is going to end well….READ FULL ARTICLE: Supernatural: Winchester vs. Winchester