Spoiler Alert, click show to read: 



This means I have to kill the roman emperor in order to complete the mission.
So I took my full stack and went straight to his location, it was Vienna. As you see in the pic I'm already sieging it.
But after taking the settlement (this includes the death of the emperor) I get this messege...
Spoiler Alert, click show to read: 




I also saved the moment before I took the settlement so I can re-do the mission.
Any solution?



P.S. Completing this mission is not really neccessary but I think it's a little strange to get this messege.