Well we don't know, but there is a comic book (Avatar: The Last Airbender-the Promise Part 1) out that is going to explain all of that, but that's only part one. It's a trilogy, so when the next two come out, THEN we'll know about Zuko's mom. You can find the first comic on youtube if you look up the following: Avatar: The Last Airbender-The Primise Part 1-1/2