He used Elizabeth Olsen's Movement Coach

Joe Locke can finally breathe a sigh of relief after the fifth episode of “Agatha All Along” is released on Disney+. That's because the installment, titled “Darkest Hour / Wake Thy Power,” ends with the long-awaited revelation that Locke's character, Teen, is actually Billy, the son of Elizabeth Olsen's Wanda Maximoff/Scarlet Witch, whose teenage superhero is Wicca. Fans expected the twist, but it still sparked shock and awe as a crown resembling a Scarlet Witch formed on Billy's head.

“It's so beautiful. I feel like I'm breathing. “I love it,” Locke told Entertainment Weekly about the big secret finally out in the world, adding that he took four doses of melatonin the night before the episode began airing so he could calm his nerves and sleep .

“I’m in the UK. The episode ends at 2:00 a.m.,” Locke said. “I knew I couldn't sleep, so I'm just going to drug myself and then wake up because my phone breaks, which is what happened. What I kept so secret and guarded with my life is now just in the ether.”

Locke's Billy/Wicca revealed himself in a somewhat villainous way when he used his power to bury Agatha (Kathryn Hahn), Lilia Calderu (Patti Lupone), and Jennifer Hale (Sasheer Zamata) in a pit of sinking mud.

“The show begins with Billy being the familiar and secondary compared to all the witches. Now we know he's a sorcerer too, and that changes things,” Locke said in response to the revelation. “Plus, we now know he has the ability to harm them. Therefore, he is now the most powerful person on the street. What does this change in the dynamics of the group and how does it change the future of these relationships?”

“At the end of Episode 5, we don’t know what happens to these witches, but he doesn’t do anything good. We played with him a lot. Does that make him a bad person? Is he a good person? “That then draws parallels to the maternal figures in his life,” the actor added. “Wanda does evil things, but she’s not necessarily evil. Agatha is debatably evil, but there's more to it than that. We know he lied to her, and we play a lot with the dynamic of his duplicity. Is the fanboy teenager façade completely false or is it actually still a real part of him? That’s what I found so interesting about playing him.”

Since Billy is Wanda's son and they have similar superpowers, it was important for Locke to study Olsen's moves as the Scarlet Witch. Key to achieving this goal was working with Jennifer White, Olsen's movement trainer, who helped develop the hand gestures for Scarlet Witch's abilities.

“We worked to find similarities between Billy and Wanda in the way they use their magic,” Locke told Entertainment Weekly. “Comic book fans know that Billy's powers are similar to Wanda's, with a few differences. That’s why we wanted to find common ground, but also our own finesse.”

Locke said that he mimicked Olsen's hand gestures in the scene where Billy first uses his powers to bury Agatha, adding, “The script said, 'With a familiar-looking hand gesture, Teen sweeps Agatha off the scene.' Street.'”

New episodes of “Agatha All Along” debut Wednesday at 9 p.m. ET on Disney+.