Plus: The actress also shares who she originally auditioned for

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A new kind of big bad is coming to Supergirl this season, one that doesn’t actually know she’s a villain.

At the close of season 2, it was revealed that another pod escaped Krypton’s destruction, housing a bio-engineered weapon called Reign, also known as a Worldkiller. In the comics, the Worldkillers are bloodthirsty, super-powered beings that set out to conquer Earth. But when Odette Annable makes her debut as the character in the season premiere, she is far from the villain fans know in the comics, appearing as a single mother named Samantha who has no idea about her true lineage. To get the scoop on Reign, EW sat down on set with Annable, who also reveals she initially auditioned for a very different Supergirl character:

ENTERTAINMENT WEEKLY: Reign doesn’t actually know she’s a Worldkiller when we first meet her. Tell us about Samantha as a character outside of that.

ODETTE ANNABLE: Samantha is a single mother, she’s a hard worker, she’s very much a working mom in the sense that she’s trying to juggle it all, as one does, as I do in real life. She loves her daughter more than words can express. They have a really special bond. What I think is really special about this storyline is it’s a slow play and you’ll get to see this whole heartbreaking story unfold in a really — they’re taking their time with it, and we have the time to do it. I think the audience is really going to hopefully relate.

How will Samantha feel when she discovers what she actually is?

It’s great because I’m discovering her journey along with these scripts. I don’t know what’s going to happen in episode 8, or 9, or 10, or however many episodes I’m doing. It’s really exciting to see these scripts and see the little bits that start to happen and start to reveal who she really is. It’s creepy.

What is it like playing both sides of her? Is it a split personality?

For right now, it’s her discovering. Clues are coming up and she’s slowly discovering that something is happening. That’s all that I know so far.

What’s it like playing that duality?

It’s interesting. The great thing about it is I’m discovering it with her. There aren’t any big reveals that are happening. It’s tiny little things that are really catching her eye and making her pay attention. It’s not something yet that she’s going to go to the cops over. It’s a very, very slow burn and all the pieces are starting to come together as we speak.

Can you tease anything about her motivations?

No, mostly because I don’t necessarily know them myself. I know that everything she does is for her daughter and I know that they have this brilliant relationship and she’s this working mom, but I don’t know where the story is going to unfold or when that left turn is going to happen. I’m very excited for it, and I know that this is such a different character than they’ve ever had on the show. But that’s really all I know. I wish that I knew more, I’m excited to know more.

What can you tease about Samantha and Kara’s first meeting?

What I said at Comic-Con, which is the truth: I have been working with Kara and we will be working together very closely, whether that’s Sam or Reign, you’ll have to find out.

They’re both struggling with what it means to be human. Can they relate?

They can absolutely relate to each other on that, on very polar opposite playing fields, but they have so much in common — not just because they’re from Krypton and from the same place, probably came in on a pod, but absolutely. Their storylines are very parallel — one will go one way and one will, unfortunately, go the other.

Will Reign cross paths with any of our other main characters?

I don’t know. I hope so. I want to work with David and Chyler and all of them. I don’t know.

What’s been the most difficult part about playing this villain?

I haven’t explored enough of her to know what is difficult yet. I haven’t even seen my suit. I’m not even trying to cover anything up. I really don’t know.

Can you talk about your casting and how this all came together?

It was really great in the way that I’ve been wanting to work with these guys for quite some time, for years now. I actually auditioned for the role of Alex, but even just in that audition that I had, I loved working with them in the room, so for this audition, I think as an actor, all your job is to portray your interpretation of the performance that you want to give, and that’s what I did and they responded to that. For me, I’m a working mom, I have a daughter, and this story is really specific to me and where I am in my life right now, so it’s a really special and important story to tell. I’m so happy that it’s part of the DC world and that I’m putting a toe in. These guys are so amazing. Andrew [Kreisberg] is so, so great to work with, he’s so collaborative, he’s so reachable, and he’s so busy and for him to make the time and for us to try to make this the best character she can be is the most important part. I think we’re doing that.

What has that training been like for this role?

Training as far as fighting? Nonexistent so far. As far as preparation, diving into the comics, there’s not much about Reign out there, so I think that we talked about this a little bit before where the pressure is off me a little bit, which is kind of nice so I can have my own interpretation of who I think this girl is.

Reign wasn’t the only Worldkiller in the comics. Is that something in the back of your mind? Have you asked if you’re the only one?

Or do I have a backup? No, that hasn’t come up. So far, it’s just me, from what I know, but it would be cool if I was fighting and had this epic showdown and all of a sudden my buddies came along to play. I mean, being bad is good. It’s always fun.

Supergirl returns Monday at 8 p.m. ET on The CW.