"I'm getting more concerned about this 'Resistance.' When you were flying over the area, did you notice the condition of the entrance to Velore and Zidus' home? I believed they were dead, but Morte thinks he might have spotted them foraging for food. If there is a 'Resistance,' I don't want Velore helping them. He's a powerful wizard, and would cause countless problems for me. Go to the home of Velore and Zidus, and kill Velore."
Exit the throne room and follow your compass to the home of Velore and Zidus, located within the remains of the forest across from Lower Avalon. When you have found it, travel down the stairs and find Velore and Zidus. Both will attack when you approach. You do no have to kill Zidus, but he will attack you in order to protect Velore. Once you have killed Velore, return to Emperor Xanthar.