Once Upon a Time Season 2 has welcomed Captain Hook on its episode Sunday. Viewers now know how -- or to whom -- he lost his arm. As new characters are introduced in flashbacks, 'Once' viewers are bugged by one character question: Who is Dr. Whale?

Remember the time when Dr. Whale told Prince Charming/David, "You're not my prince?" That was three episodes ago. Yet Dr. Whale's Fairytale Land identity still remains a mystery.

David Anders, the actor playing Dr. Whale, is confident the fans will not be able to easily guess his character's dual profile.

"Y'all are NEVER gonna guess who my fairytale character is & I ain't tellin. Just know it's gonna be worth the wait," Anders tweeted last month. Intrigue heats up!

Dr. Whale Theories: Who is this "Once Upon a Time" character?

Dr. Whale theories are exchanged in news comments and forums around the web. Here are some of the speculations:

- Dr. Whale could be Peter Pan. Early spoilers have revealed that Peter Pan will be appearing in Once Upon a Time this season. Blue Fairy could be Tinkerbell, and that is probably how they got to work together in the hospital. Children love to play doctors, don't they? In this case, Snow White could also be Wendy!

- "Whale" could be associated to Moby Dick. He probably said Prince Charming was not his prince because he has a kingdom of his own and was only caught by the curse as he got to the Enchanted Forest by accident.

- Dr. Whale could be a healer of some sort in FairyTale Land. He could also be the equivalent of a mad scientist, e.g. Dr Jekyll, of "The Strange Case of Dr Jekyll and Mr Hyde."

In the second episode of the season ("We are Both"), Dr. Whale is one of those who were about to leave Storybrooke. But after Prince Charming delivered a speech on sticking to who you really are, Dr. Whale seemed convinced. What was he thinking then?

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