SPOILER WARNING: This article contains spoilers for "Human for a Day," the latest episode of CBS' "Supergirl," which as of publication has not yet aired on the west coast.


Tonight's all-new episode of "Supergirl," "Human for a Day," saw Kara Danvers (Melissa Benoist) without her powers on a day when National City particularly needed their hero. When an earthquake struck the city, Supergirl rose to the occasion while Hank Henshaw (David Harewood) and Alex Danvers (Chyler Leigh) were trapped in the DEO with alien escapee Jemm (Charles Halford). The situation pushed Alex's suspicions about Hank to the limit, and by the end of the episode his big secret was revealed.

Hank Henshaw is J'onn J'onzz, better known to DC Comics readers as Martian Manhunter.

Created by Joseph Samachson and Joe Certa in 1955's "Detective Comics" #225, Martian Manhunter is the last surviving member of his race following a Martian holocaust that claimed the lives of his wife and daughter. After arriving on Earth, J'onzz's superhuman abilities including strength, speed, flight, intangibility, telepathy -- and, luckily for someone wanting to stay hidden, shape-shifting -- allowed him to defend his new planet as a member of the Justice League alongside DC's other marquee heroes.

During a visit to the set of the CBS series, CBR News and a small group of reporters had the opportunity to speak with Harewood, Leigh and Executive Producers Andrew Kreisberg and Ali Adler explained how the twist came about as well as what it means for the characters and the series moving forward.

Kreisberg explained that the show's writers have been thinking about Hank Henshaw's evolution dating back to when they were filming the pilot.

"We were on the set of the pilot, and we were talking about what we could do -- as happens when you're on the set of a pilot. You start seeing the sets, and you start seeing the actors, and you start thinking about, 'Well, what we could do next?' and all the different possibilities there could be. We were, all of us, just so in love with David, and so happy to have him on the show and just loved everything he was doing with Hank. And Geoff Johns and Greg Berlanti and I were standing there, and we were saying just collectively amongst us, 'It's so funny we cast David because he has those weird ears. He has a little bit of alien ears.' I don't remember which one of us said it, but it was like, 'Oh, if we were ever going to make a Martian Manhunter show or something, David would've been the perfect Martian Manhunter.' And it was Geoff who said, 'Well, why can't he be?'"

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They considered the repercussions and eventually Kreisberg and co-showrunner Ali Adler took David Harewood to lunch to share the news. It was about two weeks into filming and Harewood was initially concerned he was going to look like Shrek. Once Kreisberg and Adler assured him that would not be the case, Harewood was excited.

"Martian Manhunter is such a huge character," said Harewood. "It took me in a whole new, different direction, and it was brilliant for me because as much as I [tried], I couldn't really find an angle to play Hank Henshaw."

Hank has shown he's not a fan of Kara or her cousin Clark, and Kreisberg said there's a reason he feels that way. "Originally, Hank was going to have, obviously, a different backstory, and we said, 'Oh, actually, if he survived Mars and came here, his whole goal is to protect Earth and not let Earth suffer the same fate as Mars.' He's had to lead this crazy existence pretending to be Hank Henshaw, and he doesn't want Supergirl around. She could mess everything up. It's been really fun, and it actually fit in with how Supergirl has been evolving, and how she's somebody who's embraced her powers and stepped out into the light. In a way, J'onn is closeted, and he's afraid. Then he says in an upcoming episode when Alex is actually encouraging him to use his powers. She says, 'What's the difference between you and Kara?' And he says, 'Your sister looks like a cheerleader, and I look like a monster.'"

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Adler said the show has been been building toward this in the handful of "Supergirl" episodes that have already aired. "I think we've known about this great and amazing piece of Hank for a long time and it's really shaped our movements throughout," said Adler. "What's exciting is that we finally get to share that with people and so what's fun about that is that he has such tremendous powers so we finally get to use to our advantage all of these things that we've had to keep a little bit [hidden]. The red eyes are fun, but we really want to show off what he can do and we'll definitely use that in upcoming episodes."

The red eyes are just a small part of the look planned for the character's onscreen adventures. While the costume seen in "Human for a Day" was created though the magic of visual effects, a physical version has since been created and proved proved to the most challenging one yet for the show's costume department.

Chyler Leigh said Harewood had a strong reaction to the finished costume. "His reaction was just like -- he's like a kid in a candy store," said Leigh. "It's really amazing. He's so strong and such a calm, cool guy, but then he put on the suit for the first time the other night. We had a scene out in the desert. I've never seen a grown man make a noise like that. It was like 'Eeeeeeeeee!'"

The truth about Henshaw's history will most definitely affect his relationships with Kara and especially Alex. "With Alex, Chyler, it's been a wonderful relationship to play, because as you'll see, he promised her father that he would protect her like his own child," said Harewood. "Having lost his own child, Kara and Alex almost become his children, and he loves them. Again, you'll see that going forward, but they are his children. Having lost his own children, he has a lot of pain and a lot of melancholy, which is fantastic to play. I think these two girls represent something that's very close to him."

Leigh said that while Alex and Hank's relationship will definitely change as a result of his secret, it's more of an evolution than anything else. "It definitely adds a lot of layers to the relationship between them. You start to see that he looks at her almost as if she's one of his daughters, one of his children," Leigh said. "You learn that he had daughters and that in a huge war his family was basically eradicated, taken out. There's so many wonderful moments between the two of them where that kind of stuff comes out, where he talks about 'You're very much like my daughter.' I couldn't think of a better person to work with.' Especially in these -- we get a lot of deep emotional stuff. He's just incredible. It's been really cool watching that arc. The revelation, when it does come out, it's pretty intense."

Other things changed for Hank, too. He's finally getting to use his powers again -- including shape-shifting. "There's a wonderful flight sequence, where -- I mean, you have to remember that he hasn't used all of these powers for many years because he's been reforming the DEO and pretending to be somebody else, so I think the revelation is as much a weight off his shoulders as anything," said Harewood. "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 he's this seven-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 conflicts and issues that he has to deal with, but I think seeing Kara enjoy revealing her true nature -- there's something maybe he's perhaps a little envious because he can't quite do that."

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Kreisberg, a longtime fan Martian Manhunter, was delighted to get to introduce him on "Supergirl." "J'onn has always been one of my favorite characters from my childhood, through the 'Justice League' cartoon. Just that soulfulness and that sadness and the one who is the most frightening looking of all the Justice Leaguers and, yet, is the one with the purest heart," said Kreisberg. "Then watching this relationship that's growing between him and Alex, and him and Kara, that started out at a very gruff place, and then by the time you're getting into the meat of the season they've become this little family unit. He's become a surrogate father for them, but at the same time they're helping him become more human. It's one of the great surprises of the show for the people who are watching that there's this great -- like that old gum where you bit into it and all the juice came out? People are still unwrapping it, and they're going to get the juice."

"Supergirl" airs Mondays at 8 p.m. on CBS.