Cerdan

Cerdan was the guardian and druid master of Mordred. It is possible he was related to him, most likely as his father. He and his apprentice Mordred went to the market and tried to sell something to a stall man but the man betrayed Cerdan, apologising as the guards pursued him. He told his son to run after he used magic to close the gate. He was shortly after captured and executed by Uther. Later, while Morgana and Merlin took care of Mordred, they saw Cerdan get decapitated. Mordred reacted to this with a sonic scream that shattered glass, suggesting his strong bond with Cerdan that could be, but is unconfirmed, to be by blood. (The Beginning of the End)