SignlessAcolyte asked: Through whatever shenanigans, Azula is the avatar, and has to Hide the fact that she's the avatar, because she's terrified of Father killing her.

How does Zuko find out?

Oooooooohhhhhhhhh

He 100% finds out during a fight. They're arguing, getting on each other's nerves as usual, and Azula just unintentionally bends - the wrong element. Zuko sees her expression go from angry, to shocked, to panicked.

Zuko drags her to his room and asks her how long has she known she could bend all four elements, but Azula refuses to tell him and just keeps on begging him not to say a word about it to anyone, especially not their father. Zuko realizes she is absolutely terrified and keeps trying to reassure her that he won't let anything happen to her, but that she has to tell him the whole story for him to be able to help her.

Eventually, she'd admit that she had discovered she could bend the other three elements just a few months after she firebended for the first time, and kept it a secret so she wouldn't be seen as a traitor by their nation. She'd start crying and Zuko would just hold her tight.

After a few weeks, he'd convince her to ask Iroh for help. The old man would nearly have a heart attack, but would calm down the kids saying that he would try to convince Ozai to let him take Azula around the world to "learn from other firebending masters and see all the wonderful places their nation conquered" (learn to bend the elements so she won't accidentally revel herself. That's totally his only intention. Definitively not trying to make her a powerful avatar that could destroy Ozai).

Unfortunately, before Iroh even has the time to figure out how to convince Ozai to allow him to take his prodigy daughter away, Zuko is banished - and will only be allowed back home if he captures the Avatar.

Zuko is heartbroken not only because of what his father did to him, but also because it happened so shortly after he and Azula finally started getting along. And now he knows he is leaving his little sister all alone with a man that would kill her if he knew her secret. He had never felt worse in his life.

And he never felt more euphoric than he did the moment he realized Azula had managed to hide in his ship.