Complex sentence: Merlin, who has visibly aged little since the battle, says that Aurelius married Mira and raised Romulus as their own son, and Romulus became a wise ruler and adopted the name "Pendragon".
Split into simpler sentences: Merlin, who has visibly aged little since the battle, says that Aurelius married Mira and the two raised Romulus as their own son. He became a wise ruler and adopted the name "Pendragon".