Monday’s new episode of Supergirl featured a depowered Kara, a take-charge James Olsen and an alien adversary with a surprisingly rich comic book history, but the biggest shock of all had nothing to do with Supergirl herself, but with the mysterious Hank Henshaw. Viewers have known for weeks that Kara and Alex’s boss at the D.E.O. was harboring a pretty big secret, but now we know what it is—he’s actually J’onn J’onzz, the Martian Manhunter.

Actor David Harewood has known his secret identity for months…and has been unable to say a word about it. So when he finally got a chance to discuss it as a recent press event, he had quite a lot to say.  Here’s what we can expect from Harewood and Supergirl now that we know Kara isn’t the only well-known alien in town.

When were you told that Hank Henshaw was actually Martian Manhunter?

I was told about two weeks into the job. I knew something was changing , but I wasn’t absolutely sure what it was. Part of it was quite uncomfortable because a lot of what Hank said was exposition and was, “D.E.O., I’m this, I’m here.”

I was really pleased—Martian Manhunter is such a huge character. It took me in a new, different direction, and it was brilliant for me because as much as I could, I couldn’t really find an angle to play Hank Henshaw . It was interesting.

So, how did you change your approach to the character once you found out?

The whole idea of suppressing who you are was something I could understand, and pretending to be hiding a big secret seemed much more interesting. I was also trying to wonder why he was such a bitch to Kara. All the way through the pilot, I was thinking, “There’s something going on here. No one can hate aliens that much. There’s something that I don’t know.”

So, I was happy that it was Martian Manhunter because he is an alien, so it gave me a direction to take other than just being, “I don’t like Kara Zor-El and Superman.” That wasn’t really that interesting.

What did you know about Martian Manhunter before finding out about the role?

Nothing. What I learned from doing this job is that much of my boyhood comic book reading has all been Marvel. I grew up reading Stan Lee, reading Fantastic Four, Incredible Hulk, literally week in, week out, and I really didn't touch the Batman comics. In my day, Batman was the camp version of Batman—that was on TV when I was growing up. So, Batman was always pretty camp, but having this job—it’s made me go back to the comic books and realize that the DC Universe is much darker than Marvel. And, it’s been wonderful to journey back. It took me through the Batman story, because the Batman in the comic books is very different from the Batman in the movies. Now, people say Batman, you think Christian Bale or Chris Nolan. But actually, the comic book Batman is such a dark guy and so brutal. That’s been fascinating for me. So, when they presented me with the comic books and the model—Andrew gave me this model of this Green Martian—I was, at first, I have to say, a little bit horrified by it, because I thought, “I’m going to be playing Shrek for the next seven years.”

I have been reading Martian Manhunter comics now for the last three months, four months, and they’re just awesome. He’s such a wonderful character. You know, I’m here, I’m away from my family—my family’s in England—so I can really associate with that loneliness. He’s isolated. There’s a lot of melancholy there, and I can tap into some of that myself by just being here on my own.

It’s been a really wonderful journey as an actor to play this comic book character who is kind of macho and “I want to save the world,” was brought here completely by mistake and has learned to understand humanity and has decided to help it. I mean, he’s the center of the Justice League. That’s just awesome. I didn’t even really know about the Justice League. I mean, you look at Marvel and the Avengers, but I didn’t really know about the Justice League until I started reading these comics, and it’s been just such a wonderful journey. I’m really excited to see where this could go and to be a part of it. It’s just a great character to play. This is as good as playing Macbeth or Hamlet to me, this is a great character.

Is there anyone in the cast that you haven’t gotten to work with much that you’d like to work with more?

I haven’t worked at all with Mehcad and with Jeremy . There’s a scene in the next episode where we’ll get to do that. It’s going to be quite weird in the D.E.O. I might get territorial. But I can’t stress enough, we have such a wonderful cast. I’m so lucky to be working with such great actors. You know, this is one of those shows where you go home and watch the episode and think, “Wow, I didn’t know that she did that, and I didn’t know that was going to look like that.”

I’m really impressed with Chyler and Melissa and their physicality. It’s just brilliant. 

How is this new revelation going to affect Hank’s relationships with them?

It’s a lot of fun, actually. As you’ll see in episodes to come, there’s a lot of fun to be had. He’s a shapeshifter, so he can be whoever he wants to be. So, I think you’ll find me being other members of the cast at various points in the story.

I think, particularly with Alex—Chyler—it’s been a wonderful relationship to play, because he promised her father that he would protect her like his own child. Having lost his own child, Kara and Alex almost become his children, and he loves them.

I don’t know if you know that much about the character, the Martian Manhunter, but having lost his own children, he’s got a lot of pain and a lot of melancholy, which is fantastic to play. It gives you an enormous amount of stuff to play. I think these two girls represent something that’s very close to him.

His power set actually transcends Superman and Supergirl's, but it also has a lot of similarities. Will he be taking on that mentor role with her when it comes to using her abilities and powers? Will we see some of that?

There’s a little bit of that, yeah. There’s a wonderful flight sequence, where—I mean, you’ve got to remember that he hasn’t used all of these powers for many years because he’s been reforming the D.E.O. and pretending to be somebody else, so I think the revelation is as much a kind of weight off his shoulders as anything. It’s the fact that he can finally be himself, and I think, at times, that’s something very uncomfortable for him because he realizes Kara’s beautiful, attractive, blonde and gorgeous, and I’m this 7-foot green Martian. And, as much as I just want to be myself, it would terrify people to be confronted with this alien. So, he still has issues that he has to deal with, but I think seeing Kara enjoy—I was going to say “coming out of the closet”—but, enjoy revealing her true nature. I think maybe he’s perhaps a little envious because he can’t quite do that.