What episode does Morgana become evil?

To Kill the King is generally considered the episode where Morgana “turned evil.” Though upon closer examination, that is not exactly the case. In To Kill the King Morgana is struggling—she’s still trying to do what she believes is right—she’s just really confused about what that is—and rightly so.

How did Morgana turn evil?

Originally a kind-hearted individual, Morgana became evil after being corrupted by Morgause and being betrayed by her former-friend Merlin.