Rebecca Mader, Lana Parilla

Talk about family drama!

Once Upon a Time took familial issues to a new level last week when it revealed that the Wicked Witch (Rebecca Mader), who has cursed the fairy-tale characters back to Storybrooke with no memory of the past year, is actually the older half-sister of Regina (Lana Parrilla). Nearly green with envy (ha!), Zelena is hellbent on making her little sister pay for getting the better life.

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"I thought it was wild and unbelievable and there has to be some kind of twist behind this because it doesn't quite make sense," Parrilla tells TVGuide.com of her reaction to the big reveal. "The first time I read it, I was like, 'This can't be! I'm an only child!'"

She's not alone in feeling that way. Many fans quickly jumped online after Sunday's episode to declare that it was all an elaborate ruse. The supposed evidence is Zelena enlisting one of her flying monkeys to steal Regina's blood, which could be used to trick the blood locks used in Regina's castle in the Enchanted Forest and her office in Storybrooke. She'd only have to resort to that if she weren't blood-related, right? Parrilla debunks that theory.

"As we move forward, other things are discovered, and we learn that she actually is her half-sister," she says. "It's quite jarring for Regina. She feels completely betrayed yet again by her mother. She's not too happy about it."

Still, Zelena's threat has given Regina a renewed sense of purpose after she nearly put the sleeping curse on herself so she wouldn't have to face the pain of losing Henry (Jared Gilmore). "First of all, she really needs to find out if this woman who claims to be her sister is really her sister," Parrilla says. "When she gets her answer, there isn't much reasoning with Zelena. It results in multiple showdowns or what you could call catfights. There are a lot of fights that take place between them and a lot of learned history during those fights; stuff that is being discovered that Regina didn't know that Zelena is telling her and stuff that Zelena doesn't know about her mother."

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But Regina won't go it alone. She'll continue to work with the Charming family since they've come to somewhat trust each other after their adventure in Neverland. "Regina feels pretty comfortable working with them," she says. "She is a changed woman. She's come to a different plateau in her life, and a lot of that has to do with Henry and taking responsibility for things, consciously wanting to change and putting in the effort of making that a reality for her. She's the anti-hero, in a weird way."

It's this continuing transformation that actually gives Regina a leg up in this war against the Wicked Witch. "Regina looks at Zelena and sees a lot of herself in her," Parrilla says. "The way Regina views Zelena is somewhat like, 'Been there, done that. I used to be you.' There are even things Zelena says to her and Regina's like, 'I think I've heard that before. Oh wait, I've said that.' It's almost like a role reversal."

"Even though Zelena is the older sister, she doesn't necessarily behave as one," Parrilla continues. "She has a younger sister quality. Regina's like, 'Oh wow, there's so much you don't know. I used to be as angry as you and want to do the things you're doing.' It gives Regina the upper hand because she has this intelligence. She's smarter than Zelena."

As for whether this makes Regina the Wicked Witch of the East, Parrilla played very coy about the Evil Queen's connection to Oz. "There's an interesting twist that's coming up," she says. "I wouldn't rule out that possibility."

Back in Storybrooke, however, the fight against Zelena is much more difficult. With no memories, Regina has now teamed up with former foe Emma (Jennifer Morrison) to figure out who placed the new curse on our merry band of characters. What would've been an unlikely alliance back in Season 1 has now become the town's best hope for survival. "The combination of Emma's power as the savior and Regina as this sorceress, working together is a very powerful tool," Parrilla says.

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But there are road blocks in the way, the most heartbreaking of which is Henry, who has no memory that he grew up in Regina's care. "She gets a second chance with Henry," Parrilla says. "He doesn't know who she is, but that's OK. She looks at is as, 'Wow, that means he's forgotten everything about me, including that I'm the Evil Queen and have murdered hundreds of people!' Henry and Regina get together and spend an afternoon getting to know one another. It's really sweet. Of course, Regina wants to put her arm around him, kiss him and do all the motherly things she's always done to him, but she can't. It forces her to have a friendship with Henry. She has to dig within herself to be this kid's friend and get to know him without the pressures of being a mother."

Of course, being back in Storybrooke won't be all sunshine and rainbows since Zelena has a wild card up her sleeve. Rumplestiltskin (Robert Carlyle), the former mentor to both of Cora's daughters, is alive and being held captive by the Wicked Witch. But, as we saw in the closing moments of Sunday's episode, this Rumple is much different from the one we remember. "He's a bit off," she says. "There's something not quite right with him."

"Regardless of how many times we've seen Rumplestiltskin and the Evil Queen try to kill each other, there's an underlying love and connection between them," Parrilla says, likening the relationship to that between Regina and Snow White (Ginnifer Goodwin). "She can't hate Snow and she can't hate Rumple. They've all gotten so close, it's a dysfunctional family. No one really wanted him to die and now we see that he didn't. Learning that he's alive is a good thing all around because we need him on so many levels."

Are you excited to see the Wicked vs. Evil showdown? Are you angry that there's no Robin Hood (Sean Maguire) scoop? Don't worry, we didn't forget. There's much more to come with Parrilla next week!

Once Upon a Time airs Sundays at 8/7c on ABC.