I have a thought that I just can't get out of my head. And I realize we might find the answer in tonight's episode, so it's kind of pointless, but why not share it with you all anyway.
Is it possible that Regina and Snow are half-sisters? Hear me out. What if Regina's mother left her and married King Leopold (Snow's father)? I don't think that happened, because that's a weird area (to have married your sister's father), but the thought does nag at me. (Just FYI it's NOT incest, as they wouldn't have been related by blood.)
Anyway, we'll learn tonight why Regina hates Snow. I try not to watch too many previews, as I want to be surprised. I don't do a lot of research for the same reason: Once I read an article about the show and for several weeks knew that Graham's demise was coming, and I don't want to do that again. It was torture! But a few days ago I saw a preview clip, and Yikes! I was... "No, she didn't just say that!" It's a good one.
Be warned: If you want to be surprised, don't watch the clip.