Regina (Lana Parrilla) finally softened her heart in the past episodes of "Once Upon A Time" season 4, but her wicked side is threatening to surface again and awaken her sleeping Evil Queen-self.

In the coming episode of the hit fantasy drama titled "Enter the Dragon," Regina will have to go undercover for Snow White (Ginnifer Goodwin) and Prince Charming (Josh Dallas) against Emma Swan (Jennifer Morrison) to find out what the Queens of Darkness are up to. But will she be able to resist the temptation of going back to the Darkness while she hangs out with Maleficent (Kristin Bauer van Straten), Cruella de Vil (Victoria Smurfit), and Ursula (Merrin Dungey)? 

In the past episode of the series, viewers found out why Maleficent wants to wreak havoc in Snow White and Charming's family. Emma's parents were the reason why Maleficent lost her child back when they were all living in the Enchanted Forest, which is why she will do anything to make them pay. 

Series co-creator Adam Horowitz told TV Guide that "Once Upon A Time" fans will find out more about Maleficent's child, and how Snow White and Prince Charming caused the baby's death. 

"What we're going to see is the critical juncture of how the baby is born and what comes a bit after it's born. We're going to obviously explore how she lost her child. And at the end of that episode, I think you can see on her face that it was a very painful experience," Horowitz said. 

Also, the series co-creator mentioned that the upcoming episode will delve into the dark past shared by Ursula and Hook (Colin O'Donoghue). 

"Episode 15 will explain what he did to her. It was not sexual. It is, as he said, far worse. When you think about what would be worse than having your heart broken, I would say it was having your soul crushed. You're going to see the entire flashback of what happened. You're going to see the entire origin of Ursula," Horowitz shared.

"Once Upon A Time" season 4 episode 15 airs Sunday, March 15.