Cadeyrn is the father of Wyatt and a former general of the dark army. He refused to commit his son's soul fully to the dark cause; as a result, execution orders were sent out for them. During their escape, Cadeyrn was separated from Wyatt and hasn't been heard from since.
Gilda is also searching for Cadeyrn, as he is the only one who knows the truth about her grandfather's actions on the field of battle that led to his execution.
It is unknown whether Cadeyrn will become playable, but there is a mock-up video of his actions below: