EXCLUSIVE: 'Once Upon a Time' Stars Reveal the Secret to Outlaw Queen's 'Chemistry' and Zelena's Wicked Return

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Who's ready for some wickedly evil, yet oh-so swoon-worthy Once Upon a Time scoop?!

Now that we've already filled you in on what's next for Killian, Emma and the Charmings, it's time to shift our focus on everything that's coming up next for Regina, Robin and Zelena.

To celebrate this Sunday's 100th episode of Once Upon a Time, ET recently traveled to Storybrooke -- aka Vancouver, Canada -- and we brought back exclusive interviews with all your favorite fairy tale stars. Press play on the magical video above and read our entire article below to get all the spellbinding details from Lana Parrilla,Sean Maguire and Rebecca Mader!

WATCH: 'Once' Stars Spill the Secrets to Captain Swan and Snowing's Romance: 'It's True Love'


The Evolution of Evil: To say that Parrilla was thrilled to be celebrating Once Upon a Time's milestone episode would be an adorably huge understatement. "My heart is pounding! I'm so excited and I'm so proud of us," she gushed on the red carpet." I never thought that I, Lana Parrilla, would make it this far on any show so I'm just so grateful. I'm so proud of us."

"We have worked so hard to get here," she explained. "ABC and Disney have been great to us and most importantly is our fans. We would not be here without them, so this is such an exciting night!"

What has been really exciting is watching Parrila's portrayal of Regina over the past five seasons. From the most evil of villains to the most courageous of heroes, Regina's evolution over the past 100 episodes has been a joy to witness and, looking ahead, we still have plenty of twists and turns headed our way.

"I think she's still trying to be that hero and she's still trying to do that right thing, but it's just a matter of time before something happens and maybe she'll turn back to being evil again," Parrilla warned. "But who knows? I think her journey is a very unique one, and I think that the evolution of this character has inspired so many. It's inspired me."

The brunette beauty continued, "I've learned so much from her and it's been a joy playing all these different versions of her. From being the evil queen, to being the old hag -- Yes, I was the old hag! People didn’t know that -- to Ursula, and to all these different characters that I've been able to play just in one character. It's been a dream job."

MORE: 'Once' Bosses Spill on True Love's Kiss and the Same-Sex Romance!


Outlaw Queen's Chemistry -- Revealed!: When we caught up with Maguire, the actor could not stop gushing and blushing about what an "absolute joy" it has been to work alongside Parrilla for the past three seasons.

"I've been very lucky. I've never really had too many actors that I didn’t get along with, but when you get along really well with somebody, it changes the chemistry," he revealed. "It changes the way that we interact with each other. Even the way that we touch each other, you can only really do that when you feel comfortable with somebody."

Maguire revealed that his wife, Tanya Flynn, and Parrilla's husband, Fred Di Blasio, also have a great friendship, which helps makes their on-screen rapport even better. "I think the fact that our partners really get along with each other just makes life great and easy," he said. "When you see it on screen, you can tell when people get along, and you can tell when they don’t, and Lana and I just kind of hit it off from day one."

And it's clear that Parrilla feels the same way about her arrow-wielding co-star. "Sean Maguire, I love him to bits. He's just a sweetheart and just so much fun to work with," Parrilla beamed. "And it's really beautiful to see Regina in love. That's really what she always wanted was love -- family and love -- and now she has that."

So what is it that makes this couple so magical? "They're both damaged people with a bit of a dodgy past and they've got darkness in their pasts," Maguire explained. "So I think there's something about them that there's a sort of redemption -- there's hope. This show is essentially about hope and I think this couple shows that maybe if you just get through that tough, dark challenge, then there's sunshine around the corner. I think people really kind of root for them and it's a lovely thing to be a part of."

MORE: 'Once' Scoop on Regina and Robin's Baby Mama Drama With That 'Vile Villain'!

A Wicked Return: Despite being banished to Oz (again!) by Regina, it's clear that we haven't seen the last of our favorite wicked witch. "I just won't die," Mader confessed to our camera with a laugh. "Sorry. You can't get rid of me."

"Zelena's just on a really interesting journey that I think the fans are really going to really, really love," she added.

And things are only going to get even more interesting when we have Zelena, Regina and Cora all back together for one wickedly-evil family reunion. "I'm excited that Cora is coming back. My mummy is coming back! That's very exciting," she dished. "[That reunion] is so very, very wicked you're going to love it. It's really amazing."

The British beauty revealed that all Once Upon a Time fans are in for a real treat as we embark on our next deadly adventure. "This half of the season is just so good," she spilled. "Being in the Underworld and dealing with people's unfinished business and people coming back -- I feel like it's a throwback to season one with people working out their relationships and original characters. I think the fans are going to love it. I really do."

WATCH: 'Once' Cast Laughs About 'Warped' Romantic Relationships in Storybrooke!


Baby Mama Drama: Let's be honest, not too many characters on TV can say that they have slept with their sister's boyfriend while disguised as said boyfriend's ex-wife -- and we totally called Mader out on that tangled romantic web!

"You could say that you can't make this stuff up but somebody did!" she exclaimed with a laugh. "It's unbelievable, and you're the first person to say it. Congratulations! You completely nailed that. That was amazing, I honestly don’t think that I could have repeated what you just said. But yes, that happened. That happened in the world of Once Upon a Time and It was absolutely bonkers but if somebody's got to do it, I'll do it."

And as a result of that twisted love triangle, we now have a sweet little green bean, who doesn’t have a name yet! So are we going to be discovering Baby Hood's first name this season?

"I think so," Mader confirmed. "I don’t know what it is yet, but we must name her at some point. Maybe I'll name her after you. Leanne Hood -- It's got a ring to it."

We might be a little biased, but that sounds great to us!

Once Upon a Time's 100th episode airs Sunday, March 6 at 8 p.m. ET/PT on ABC.

Keep it locked to ETonline all week for even more exclusive Once Upon a Time interviews from the red carpet and tweet @LeanneAguilera with your favorite moments!