An upcoming episode of Once Upon a Time will center on the Wicked Witch (Rebecca Mader) and the details of what made her so green and wicked.

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The Wicked Witch was introduced in the final minutes of the Once Upon a Time midseason premiere that aired Sunday night. The iconic villain was shown dropping Regina's (Lana Parrilla) blood into a bottle, noting that while Regina is indeed an evil queen, "wicked always wins," referring to herself.

Once Upon a Time will soon be delving into what made the Wicked Witch, a.k.a. Zelena, so wicked, according to Parrilla.

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"There's some real deep-rooted issues there, with this [Zelena] character," Parrilla told E! Online in a Monday report. "It manifests in jealousy, it comes out in envy, but there's some deeper issues there that I can't share with you."

Zelena's big backstory episode is set to occur in episode 16, which is titled It's Not Easy Being Green. Once Upon a Time co-creator Edward Kitsis previously told The Hollywood Reporter that the next few episodes will feature an examination of the Zelena-Regina rivalry.

"When we learn more about the Wicked Witch and her backstory and what happened, we'll understand that what she has against Regina is a global problem and an internal problem," Kitsis said in the report. "Those two are definitely going to get into it."

Once Upon a Time season 3 airs Sundays at 8 p.m. on ABC.

Watch the promo for the next episode of Once Upon a Time here:

Tags: Once Upon A Time television ABC