Kyran was stunned after hearing Cade. He only thought Nolan's an Arch Magus or a newly advanced Legendary, but never thought of him as someone close to becoming a Sovereign.
But this possibility raised a lot of questions.
If Nolan was already a Sage why did he have to hide his strength? His magic pressure alone could easily send his enemies to their knees. Why did he not offer to save the Regis right from the start? Why did he let things escalate?
Nevertheless, even with these questions, Kyran could more or less guessed the answers.