How Supergirl's Season 4 Finale Sets Up SPOILER For a Villain Turn in Season 5

Tonight's episode of Supergirl had some surprising turns as the titular heroine and her allies attempted to thwart Lex Luthor's ultimate evil plan, but it turned out that Lex's plans were even more detailed and complex than anyone expected -- leading to a stunning reveal that is sure to create major drama in Season 5.

Spoilers for tonight's season finale of Supergirl, below.

Most of the action in tonight's episode centered around the attempt to stop Lex from unleashing his ultimate plan, which was to use aliens to power a satellite that would destroy Argo and thus, Superman. It ends up being a group effort with Nia, J'onn, and Brainy working to overload the core of the satellite so it can never launch while Lena and her mother try to deal with Lex in Washington. Ultimately, Supergirl ends up fighting Lex and he opts to fall to Earth instead of letting her save him, which in turn leads Lex and Lena to a confrontation on Shelly Island where she shoots Lex, deciding to kill him once and for all, but the iconic villain has one more trick up his sleeve.

Lex, as he dies, turns on footage of various times when Kara has used her Kryptonian powers and, thus, reveals to Lena that Kara is Supergirl, but more than that that all of her friends have known and have been lying to her all this time. While Lena pretends later that all is well -- and doesn't reveal that she knows the truth -- the last we see of her in the episode she's in her office at L Corps, drinking and shatters a photo of herself with Kara with the glass.

Now that Lena knows Kara's secret, it could set up for some major drama in Season 5 as well as potentially set Lena up for a major villain turn. That is something that fans of Supergirl have expected since Lena's first appearance on the series (and something that we theorized could potentially be coming in Season 3 ourselves). It's also something that Katie McGrath herself said during a previous visit to the show's set she would prefer be different.

"I'd like it to be different," McGrath said during a visit to the Supergirl set. "I don't think it will be what you expect because it's never what you expect. I think they've set her up to be so sympathetic I find it difficult to think how ultimately evil and Luthor she can get."

Now it looks like fans will get to see how evil and Luthor Lena can get in Season 5 -- provided the lead up to "Crisis on Infinite Earths" doesn't complicate things first.

Supergirl will return this fall Sunday nights at 9 p.m. ET after Batwoman on The CW.