Once Upon a Time Once Upon a Time

She murdered her father, squeezed the life out of her lover's heart and conjured a curse that ripped the lives of thousands of people from their homes, erasing their memories and leaving them stranded in a foreign world. What makes Once Upon a Time's Evil Queen so evil?

That soon will be answered on the ABC fairy-tale drama, but portrayer Lana Parrilla teases that the origin of her malevolence springs from one place. "It's one particular moment," she tells TVGuide.com. "It's one thing that just explodes and branches off into all these other little things, but it's one big f----up that changes her life."

"We'll go back in time in fairy-tale land and see who she was before she became this evil queen," she adds. "The big secret will be revealed."

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Before she was sending the Hunstman after Snow White (Ginnifer Goodwin), she was married to Snow's father, King Leopold (Richard Schiff), though their dysfunctional union was the catalyst for her hatred of Snow. "There is an episode coming up where you do see the king and queen together and you can see the hardship between them," she says. "You learn of how unhealthy and unsupportive that relationship was. How he always favored his daughter more than her."

Whether she truly loved the king or was only seeking his status remains to be seen, but the Evil Queen is capable of love as we'll come to learn that she had a previous lover she truly cared for. "It is someone that you've met before," she reveals. "You see this really soft, vulnerable side to her. Even her voice shifts with a softness to it. She wants to love, it's just difficult for her. Once she has it, she doesn't really know how to sustain it or stabilize it."

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Her inability to love was proved when she killed off the only man in Storybrooke who's ever shown her affection. "I don't think she feels good about what she did," Parrilla says of Regina killing Graham (Jamie Dornan) in the midseason finale. "You see a tear coming out of Regina's eye when she crushes the heart, which, to me, is very telling. You can see that this was not an easy decision for her."

Once Upon a Time returns Sunday at 8/7c on ABC.

Watch the first eight minutes of Once's return: