Who Is Nimue on Once Upon a Time?

According to Arthurian legend, Nimue is referred to "the Lady of the Lake" and was Merlin's great love. He allegedly fell head over heels and taught her all of his magic secrets.

After learning all there is to know about magic, the story goes that the Lady of the Lake used her power to trap Merlin in a tree. While we wouldn't put it past the writers to throw in another complicated relationship on the show, this theory does seem a little odd since we already know that it's the Dark One who traps Merlin in the tree to begin with.

Merlin sheds a tear for his lost love, but maybe he is actually shedding a tear for the darkness that consumed her. Is it possible that Nimue is actually the original Dark One? The show has been known to throw some major curve balls before, so this theory could totally be true. Guess we will just have to wait until Sunday night to find out for sure!