Board Thread:Spoilers!/@comment-6175354-20140420035659/@comment-1293767-20140424052751

Stonicus wrote: It's been said this new curse is the same curse as before... It's also been said a few times that the curse must be cast by a daughter of Cora... in keeping with the "rescue" theme of the second curse and that our good guys did it, then it *has* to be Regina, unless Cora has yet another unknown daughter.

The first curse needed to be cast by Cora's daughter because that's what Rum saw when he got glimpses of the future. He just didn't realize she had two until much later on.