Board Thread:General Discussion/@comment-5825802-20140422223811/@comment-24386552-20140423155255

Zelena being Regina's half-sister through Cora. (Minus the fact that Rose McGowan was already added to the returning cast before the Witch Hunt episode, aired) Snow white's mother caused Cora (the evil queen's mother) to become very evil, which rubbed off on her daughter causing her to become the evil queen.