South Vern Chaos Line Question: "Wicked Kyrza" boss?

I haven't been able to find any info on this looking everywhere, but does anyone know what the deal is with the prompt at the end of the south vern chaos gate once you get all 3 keys? The quest will say

"Chamber of Chaos
- Defeat the Wicked Kyzra
- or defeat the Shadowed Kaishur "

I've done the gates ever since they came out, but I only ever get the shadowed kaishur boss at the end, and I'm not sure where or how to find "wicked kyrza." I even ran around the dungeon before triggering the final boss to see if I missed something, but didn't find anything. Anyone know?