Supergirl: Lena Finally Confronts Supergirl About Her Betrayal in "Tremors"

The fallout of Lena learning the truth about Supergirl's identity has been a major component of The CW series' fifth season thus far. While Lena has presented things as being fine between the two after Supergirl confessed to her just before her Pulitzer ceremony, the reality is that Lena has been conspiring behind her back, using the Girl of Steel to help with her own plans to "better" humanity. Tonight, however, the truth about Lena is revealed -- as well as at least part of her plan for humanity.

Spoilers for tonight's episode of Supergirl, "Tremors," below.

In tonight's episode, Supergirl takes Lena to the Fortress of Solitude as they go to find one of Lex's more dangerous weapons that Superman has stored there as they endanger Kryptonians. Lena has ulterior motives, though. She is hopeful to find something there that she can use for her plans and sure enough, she does. Lena happens upon Myriad and Supergirl explains its use and how turned everyone into zombies that acted to her aunt's evil will. This is the exact device Lena needs as it will help her spread her own controlling technology around the world so that people cannot hurt or lie to one another.

After a brief distraction in the form of Rama Khan coming to the fortress in an attempt to collect Lena and the Medallion for Leviathan, Lena moves to take Myriad and Supergirl catches her. It's then that Lena reveals the truth. It was Lena, not Supergirl, who killed Lex and, more than that, Lex told her about Supergirl. Devastated that her so-called friend had spent years deceiving her despite knowing her history of betrayal, Lena unleashes her pain and rage on Supergirl and admits that she is using her and that she is doing it because she wants her to hurt as she did. She then imprisons Supergirl in the Fortress before leaving with Myriad, her plan full steam ahead.

The episode ends with a devastated Supergirl alone in the Fortress.

It's a heartbreaking moment as the truth sinks in for Supergirl, but it also pushes forward what series star Melissa Benoist has previously described as a "fight for Lena's soul" this season.

"This season's going to be a fight for Lena's soul," Benoist said, who was surprised and heartbroken by how Lena found out Kara's secret. "I was devastated that it was Lex Luthor that told her. That was such a shot in the heart to Lena, a character that my character loves so dearly. It was painful."

McGrath herself has also previously said that she never wanted Lena to learn Supergirl's identity, though Benoist said she always knew it was going to happen and she thinks it's important to explore.

"To me, that would be wishful thinking, but I always knew it was going to happen," Benoist said. "I think part of what we are trying to do on Supergirl specifically, too, is explore relationships between women, and friendships, and sisterhoods, and how we treat each other, how we communicate that's different between men and women. I think their relationship is singular already because they're such close friends and you get to explore that. This is only going to make that conversation a little more complicated."

And things are only going to get more complicated next week. The preview for "The Wrath of Rama Khan" reveals Lena has a Kryptonite-charged device -- one that could threaten Supergirl.

Supergirl airs Sundays at 9/8c on The CW.