'Supergirl' Star Melissa Benoist Talks the Impact of Lena's Secret Experiments

This week's episode of Supergirl saw Lena Luthor take the next step in her Harun-El experiments to turn human beings "super" -- human trials.

It's a development that feels like a point of no return for Lena (Katie McGrath), just the latest questionable decision she's and secret she's kept on what feels like a path to her taking a dark turn and becoming just like the rest of her family. While Lena hasn't gone full Luthor just yet it, the secrets she's keeping could have major implications for her relationships -- particularly with her best friend Kara.

"It's a very Luthor secret to keep," Supergirl star Melissa Benoist told reporters during a recent visit to the set of The CW series.

And by that "very Luthor secret", Benoist is referring to the dynamic not just between Kara and Lena, but of Lex Luthor and Clark Kent as well -- and it sounds like Lena and Kara are headed down a similar road.

"I think what's so fun about exploring a Luthor and a 'Super' relationship is the slow burn of it," Benoist said. "I love that we're telling in the way that Lex Luthor and Clark Kent were friends before they were enemies. I love that we're telling that story, too. I would expect that it will be a really slow burn: that realization, reveal."

Of course, as fans of Supergirl know, it's not just Lena who is keeping secrets. Kara has yet to come clean with Lena about her own dual identity as Supergirl. It's not surprising considering how Supergirl and Lena clashed last season, but it sounds like Kara plans to keep her Supergirl identity a secret from Lena for the foreseeable future.

"I don't think it would be a Kryptonian story without stories like that," Benoist said. "That's just the nature of Clark Kent and Kara Danvers that they have to toe that line. That was the decision Kara made at the end of last season, the end of season three, that she wanted to embrace her life, messy as it could be with two identities, she didn't have to choose. So I think she's always going to be juggling both of those things."

Do you think Lena has passed a point of no return? Let us know your thoughts in the comments.

Supergirl airs Sundays at 8 p.m. ET on The CW.