Spoilers ahead for tonight's episode of Supergirl, titled "Human For A Day."

Additional reporting by Ashley Robinson.

Tonight's episode of Supergirl shocked fans by not only revealing that DEO director Hank Henshaw is J'Onn J'Onzz, the Martian Manhunter, but by revealing his appearance and costume as well.

You can see it above.

"The whole idea of suppressing who you are was something that I could understand," said actor David Harewood, who plays the character of Hank Henshaw/J'Onn J'Onzz on the series. "And pretending to be -- hiding a big secret -- that was, obviously, much more interesting and I was always also wonder[ing] why he was such a bitch to Kara? [Laughs] All the way through the pilot I was thinking, 'There’s something going on here. No one could hate aliens that much. There’s something that I don’t know.' so, it was [one of the] reasons I was happy it was Martian Manhunter because he is an alien. 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 to me."

He added that J'Onn, being a character who lost his child, sees Kara and Alex as kind of a surrogate family, and he's looking forward to exploring that relationship more.

Supergirl returns for its midseason finale on Monday, December 14 at 8 p.m. ET/PT on CBS.