Anger
It took Ben a few hours to digest the news surrounding his disciple, but after talking to various sources and filtering out the parts that obviously sounded fake, Ben pieced together the following information.
1)That his disciple had declared himself to be the new ruler of the East and the leader of all rebels, making him state enemy number one.
2)He was currently in the process of wiping out the current nobility of the East, with him having captured 90% of the Eastern Duchy already.
3)He was directly challenging the territorial integrity of the Empire, making himself a bigger enemy of the state than Ben in his prime, as while Ben only killed the Emperor, Leo was taking away the land that made the man holding the throne of StrongHaven Emperor.