While Sir Casimir was in the Chapel, he struck a beggar and killed him, this not only caused the Gauntlets of the Crusader to fall off his hands, but Stendarr also cursed Casimir and all his descendants.
When the Hero talks to him, Kellen will explain that, while he could live with the effects as a young child, things have become more difficult as he grew older. He hoped that visiting the Chapel and lifting the gauntlets would somehow lift the curse. However, when he tried to lift the gauntlets they would not budge and he gave up. A priest, Areldur told him he could stay at the Chapel for as long as he needed. While at first he thought it was out of pity he soon felt there was more to it, like Areldur was apologetic. Guilty, even.
The Hero can question Areldur with Kellen’s suspicion, which will reveal that Areldur has known all along how to remove the curse, but has been to afraid to do what is needed. In order for the curse to be lifted, another person must remove the curse, and must take it on themselves.. The Hero at this point can to the Altar of Stendarr and pray for a way to lift the curse on Kellen, after receiving a means to do so, they can go to Kellen and remove the Curse of the Consumed from him and in turn receive the curse.
Kellen will rejoice at his new energy and run around the undercroft screaming in joy. When he calms down he will thank the Hero and run out of the Chapel, ready to see the world that he could not while cursed.
Kellen can be found in the inns across Cyrodiil after removing the curse. On rare occasions, while travelling the player will receive a message "Kellen is Unconscious" randomly in the wilderness, indicating that in his travels Kellen encounters and engages in combat with various monsters and bandits—and loses.