Warning: This article contains spoilers from Agatha All Along episode 5, “Darkest Hour / Wake Thy Power.”

Not even 12 full hours after Marvel dropped the fifth episode of Agatha All Along on Disney+, Joe Locke looks euphoric. It’s almost like the anxieties from keeping a big secret for more than two years just aren’t there anymore. “It’s so nice. I feel like I’m breathing. I love it,” the actor tells Entertainment Weekly amid one overt exhale, sitting on the couch of his U.K. home in front of bay windows that overlook the street. The previous night, though, was a different story.

With the release of “Darkest Hour / Wake Thy Power,” the episode in question, came the long-anticipated reveal that “Teen,” the mysterious character Locke plays on the show opposite Kathryn Hahn’s Agatha Harkness, isn’t your average goth kid hoping to gain magical powers by joining a coven down the Witches’ Road. He’s actually Billy, the grown-up son of Elizabeth Olsen’s Wanda Maximoff/Scarlet Witch and the super-teen known as Wiccan in Marvel comics. The young Julian Hilliard played kid Billy in WandaVision.

The big unveiling came in the final seconds of Wednesday’s installment when he revealed his magic and sends Agatha, Patti Lupone’s divination witch Lilia Calderu, and Sasheer Zamata’s potions expert Jennifer Hale into a pit of sinking mud after the show’s titular antihero killed a member of their group, Alice Wu-Gulliver (Ali Ahn) — the jury’s still out on whether it was accidental. The final shot showed Locke looking directly into the camera with a blue Scarlet Witch-esque crown now on his head to the sound of Billie Eilish’s “You Should See Me in a Crown” — a moment Locke calls “perfect,” having watched an early screener back in June.

It’s a historic moment for Marvel storytelling, as Billy is the most prominent LGBTQ+ character the cinematic universe introduced thus far. Locke is well aware of that inclusion. He took four doses of melatonin the night of the big reveal to get to sleep. “I’m in the U.K. The episode drops at 2:00 a.m.” he says. “I knew I wouldn’t be able to sleep, so I’m just going to drug myself and then wake up to my phone blowing up, which it did.” He was, admittedly, nervous for the moment, adding, “The thing that I’ve kept so secret, guarding it with my life is now just in the ether.”

Marvel fans clocked early on that Locke would be playing Billy/Wiccan, partly because there is a severe lack of gay comic book characters that have some kind of connection to Agatha to choose from, and partly because certain leaks from the production seemed to prove the theory true. There were also clues on the show itself as the first few episodes started streaming. Locke points out one such Easter egg: the image of Wanda’s crown is stitched onto Billy’s sweater, though the actor acknowledges it’s on the back, so audiences might not have caught it.

From day one, showrunner Jac Schaeffer knew of that theory chatter permeating the internet and imparted unto her actor that the shock wouldn’t be the Billy reveal itself. “You can do the most unsurprising thing in the most surprising way, and that’s how you hook an audience,” Locke remarks.

Now that the audience is hooked, “The show starts getting real,” he continues. “The show starts with Billy being very much the familiar, the secondary to all the witches. Now we know he is also a witch, and that changes things. Also, we now know that he has the ability to cause harm to them. Therefore, he is now the most powerful person on the Road. What does that change in the dynamic of the group and how does that change the future of those relationships?”

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The rest of the nine-episode season is Locke’s favorite material, especially this week’s episode 6, which will explore Billy’s true motivations, why he’s on the Road in the first place (hint: it’s not to achieve power like he said), and his backstory. A new midseason trailer for Agatha All Along (released after this article was originally published) teases that backstory.

Billy mentioned that a lot happened to him at the age of 13, and the footage features a glimpse of one Billy Kaplan, born to Jeff and Rebecca Kaplan of Eastview, in a car crash during the events of WandaVision. This is our strongest clue yet as to how Hilliard’s younger Billy Maximoff disappeared when Wanda lifted the hex over Westview but is now able to stand before us fully grown on the Witches’ Road.

Episode 7, Locke also notes, “is the best episode of the show purely because of Jac Schaeffer’s incredible form and storytelling.”

“We talked a lot about playing with the gray area,” he recalls of charting out the character’s path with Schaeffer. “At the end of episode 5, we don’t know what happens to those witches, but he’s not doing a good thing. We played a lot with, does that make him a bad person? Is he a good person? Which then draws parallels to the motherly figures in his life. Wanda does evil things but isn’t necessarily evil. Agatha, questionably, is evil, but there’s more to that, as well. We know that he’s been lying to her, and we play a lot with those dynamics of how duplicitous he is. The facade of the fanboy teen, is that completely fake or is that actually still a real part of him? This is the stuff that I found so interesting in playing him.”

Locke wasn’t well-acquainted with the Billy of Marvel comics, who was born Billy Kaplan as the reincarnation of one of Wanda’s two children that she created with magic. But when he booked the job, the gatekeepers at Marvel gave him access to that comic book history in which Billy becomes a formidable sorcerer as a member of the Young Avengers, a team of younger superheroes. Locke flashes towards his Zoom screen the cover of the giant paperback omnibus collection of Young Avengers, featuring artwork from the Children’s Crusade, one of the more popular comics featuring Billy. Locke clarifies that Agatha All Along is not following the blueprint of that narrative — or any one specific comic, for that matter.

More informative for him was working with Jennifer White, the movement coach who helped Olsen formulate the hand gestures for Wanda’s abilities. “We worked to find similarities in both Billy and Wanda, the way they use their magic,” Locke says. “Fans of the comic corner know that Billy’s powers are pretty much the same as Wanda’s with a few differences, so we wanted to find similarities with that, but also his own finesse.” Billy’s big moment blasting Lilia and Jen off the Witches’ Road, for example, was meant to emulate one of Wanda’s arm gestures from Avengers: Age of Ultron. “In the script, it was written as ‘with a familiar-looking hand gesture, Teen swipes Agatha off the Road,'” he recalls.

Locke says he hasn’t met Olsen in his travels as an actor just yet, but in the back of his mind, he’s thinking about what the future might hold for both himself and Billy beyond Agatha All Along. For instance, the MCU seems to be setting up the debut of the Young Avengers after a post-credits scene for 2023’s The Marvels.

“In my ideal world, Billy would become the next head of the Avengers and be in every Marvel thing ever, but there are higher things at play,” Locke says. “I had the most amazing experience filming on Agatha and being a part of the Marvel family and would love to do that until the day I die. But who knows? I don’t. I’m sure someone does.”

This article was updated with the release of a midseason trailer for Agatha All Along.