In the final episode of the Season 1, Vilgefortz stands as one of the mages opposing Nilfgaard. During the battle of Sodden, he duels Cahir and looses, however, he manages to escape. We can see him later stumbling on a group of dead Nilfgaardian troops... and one man who seems to know him. That person calls to Vilgefortz for help, but he instead grabs a mace and kills the wounded man.
Who was that victim? Was it one of the Nilfgaardian mages? One of the defenders that somehow witnessed Vilgefortz humiliation?