For an actor, playing one role on a critically-acclaimed television series is thrilling enough. Playing five roles and counting? That’s enough to make anyone nervous.

For Orphan Black actor Ari Millen, however, the nerves are always a part of the responsibility of playing a character. Cast on the show for its second season, he wasn’t aware until well into shooting that the creators were thinking up something a little more ambitious for him. As we sit down to chat midway through the show’s third season, Millen has lots to say about his process for creating the Project Castor clones and the thrill ride that is the rest of Season 3.

(Beware: there are some spoilers for Season 3 below!)

“I don’t think [Orphan Black creators] Graeme Manson and John Fawcett knew that my role was going to evolve either, at first,” Ari Millen tells me with a chuckle.

A Kingston, Ontario native, Ari Millen attended Ryerson University’s Theatre School before signing on with a talent agent to pursue acting. With some plays, independent films and guest starring roles on television under his belt, Millen was a fan of Orphan Black before auditioning in 2013. Millen, originally cast as loyal Prolethean Mark Rollins, had his role on Orphan Black expanded with the Season 2 finale reveal of Project Castor, a set of male clones developed alongside the female clones of Project Leda. Now, in the middle of Season 3, Millen has added four more characters to his roster: Rudy, Seth, Miller, and Parsons. It’s a dream come true for the actor who was once just a fan of the show.

“I watched the first season of Orphan Black before I was cast, so I was already a fan. I loved the show. Being cast on the show was a huge thing for me, and then to all of a sudden know that I’m going to get to create multiple characters at once… it’s just something I never thought possible.”

Especially given the original intended plan for the character of Mark. One of the Proletheans keeping Helena captive, Mark was originally intended to die in the sixth episode of Season 2 at the hands of Paul Dierden (Dylan Bruce). The decision to keep Mark alive, Millen says, was certainly a surprise.

“I read episode six, waiting for my epic death, and it didn’t come,” he shares. “At first, I was sort of disappointed—I wanted this crazy scene. But then I realized, ‘Oh, wait, he gets to keep going! He’s not dead!’ So I kept reading the episodes and I wasn’t dead… I wasn’t dead… so I thought, ‘Hey, great.’. And then I had a very good conversation on the phone with Graeme [Manson] one day, and he told me what they were planning.”

For many actors, the weight of stepping into multiple roles at once would certainly be daunting. For Millen, however, it was an exciting phone call—not scary in the least.

“The nerves I had came along with a feeling of, ‘Holy crap, I’m really going to get to do this!’. This is a dream come true,” says Millen. “Anytime I get cast in something, I put a certain amount of pressure on myself because I want to do a good job. With this, I couldn’t ask for more. It was just sort of like, ‘Okay! Here we go!’”

Playing the role of the Project Castor clones is a little different than the work Tatiana Maslany does to portray the show’s Project Leda clones. Unlike the female clones of Orphan Black, the male clones were raised self-aware and were all raised together; therefore, their differences are much more minute. This presents a different acting challenge for Millen, and he worked hard to get it right. The first step? Focusing on differentiating between his characters.

“Thanks to Season 2, I already knew who Mark was, but throwing more characters into the mix made it tough. It wasn’t easy!” Millen reveals. “Going into it, I knew the clones were self-aware and that they grew up together. I’m an only child, so it was really interesting for me to wonder what it would have been like if I’d had a brother. One of the starting points for me was figuring out the pecking order of the brothers—who’s the eldest, who’s the youngest, things like that. Then I started developing their personalities from there, and working out the dynamics between them. I also had to work out the dynamics between each of the clones and their mother, and between each of the clones and Paul. There were also all the visuals to go along with it. As the hiatus went on, I was able to hound Graeme and John about them, and learned more through pre-production meetings. It was a really interesting process, finding the little things to assert their independence and their uniqueness. “

There was one other person who helped Millen and the show’s creative staff when it came to bringing the Castor clones to life: Millen’s clone double, Nick Abraham. Abraham is an actor who attended the Ryerson Theatre School alongside Millen, and when Millen learned he’d be needing an acting double for Orphan Black, Abraham was the first person who sprang to his mind.

“He was always my first choice. I went to him as soon as I realized I’d need a clone double, and said to him, ‘Hey, if you’re interested, you’re who I’d want. Tell your agent to submit you,’” Millen shares. “He was interested, he was my first choice, and he just so happened to look the most like me out of everyone who was seen. And it all worked out!”

Orphan Black employs two clone doubles—Abraham is Millen’s, and Tatiana Maslany works with actress Kathryn Alexandre in all of her clone scenes. The scenes are filmed with Millen and Maslany in one of their roles, playing opposite Abraham and Alexandre. Then, the roles are switched—Maslany and Millen play another clone in the scene, and Alexandre and Abraham step in to play the clones opposite them. Maslany and Millen’s characters are all merged into one scene together in post-production. Having acting doubles not only helps the visual effects artists put together the scene, but gets better performances out of Millen and Maslany—actors will almost always give a better performance when they’re acting against another human being. It’s hard work, but it’s almost harder for Abraham and Alexandre: they do all the work of Maslany and Millen, but see none of the payoff of their own work onscreen.

They are, in a word, essential. “Nick [Abraham] and Kathryn [Alexandre] are so invaluable, and they inform the characters just as much as [Tatiana and I] do,” Millen says. “Nick and I spent a lot of time brainstorming about the Castor clones, and it was wonderful to have known him beforehand. We could hit the ground running because we had that familiarity—there was no need for any icebreakers. I wanted to know what he thought, and because we knew each other, there were no reservations on his part when it came to telling me his ideas. There were certain things he did with the characters this season that I just never would’ve thought of. I’m so happy I had him as my clone double, because his choices made the characters that much better.”

Having someone else to bounce ideas off of while developing characters is a great asset for an actor, and it got Millen thinking more and more about the pecking order of the Castor clones.

“I remember thinking, a few weeks into Season 3 after getting to know the clones a bit better: ‘I think Mark is superior to Rudy in rank.’ We show Rudy as sort of this confident, cock of the walk character, but I thought Mark outranked him, especially with how we saw him in the premiere of Season 2. How interesting would it be to see Rudy bow to Mark?” Millen shares. “So I brought the idea to Graeme, and he said, ‘Just you wait, Ari. We’ve got you covered.’ And sure enough, there was the scene with Mark and Rudy in the barn in Episode 4. It was just so nice to be on the same page. There were a couple times during filming where I’d have a thought about one of my characters, and Graeme and the writers were already there. It was so interesting.”

The more Millen got to sit with the characters, the more excited he would get as each new script was handed to him. Unable to pick a favorite clone to play, Millen focused on favorite scenes from each episode for his characters. Revealing new things about the clones, or getting to explore a new dynamic, are always among Millen’s favorite things to do onscreen.

“On Day 2 of shooting this season, we shot the scene with Rudy in Felix’s loft, with the Xs over his eyes. And at that point, I thought, ‘This is my favorite scene. We’re never going to top this. I can’t believe I have to play my favorite scene so early in the season!” he recalls. “But then we shot the scene with Rudy killing Seth, and I thought, “Oh, wait, this is fantastic! I like this even more!”. Then in Episode 4, they wrote the scene with Mark and Rudy, which was so exciting to play. I couldn’t even pick a favorite episode, let alone a favorite clone—I’d just pick favorite scenes in every episode. It was all a thrill.”

And the most exciting scene in Episode 5, for Millen, was Mark’s return to Castor’s home base.

“The scene between Dr Coady and Mark in that episode was just wonderful,” Millen says. “Finding all the different dynamics between the brothers and their mother was very exciting for me, but I think the dynamic between Dr Coady and Mark is possibly the most complicated. That scene was so great, because it’s quick and loaded and intense. These boys have mama issues!”

According to Millen, Episode 5’s scene with Dr Coady certainly isn’t the last intense moment of the season. Orphan Black is a wildly fast-paced show, with clues and new revelations appearing left and right, and it seems like the show’s writers are ready to start giving audiences some answers.

“Questions that people have been dying to know since the show started in Season 1 are going to come up again. Season 3 is peeling back some of the layers,” he reveals. “We’re going to be getting some answers to the questions we’ve been asking all along… and with those answers are going to come new questions, of course. But there’s something really satisfying about it all, because we’re finally going to start learning the ‘why’. We’ve got one or two big reveals coming at the end of this season that I can’t wait for everyone to see.”

With Season 3 of Orphan Black halfway through, fans are dying to figure out where all of this is leading and to learn the fates of their favorite clones. Though he’s tight-lipped about the remaining episodes of the season, Millen has one promise for the show’s fans:

“Clone Club is going to lose it!”

Prepare yourselves, fans of Orphan Black: this thrill ride is only half over! If Ari Millen has anything to say about it, these last five episodes are absolutely not to be missed.

“Orphan Black” airs Saturdays at 9/8c on BBC America and SPACE.

Aside from his roles as Project Castor, Ari Millen can be seen in several upcoming horror and supernatural independent films. To keep up with Ari and his other projects, follow him on Twitter.