Keirran is Ash and Meghan's son. He is first formally introduced in The Iron Knight in Ash's vision of a possible future. However, a few references are made about him in the previous books. Keirran is 75% human and 25% Fey, due to the fact that Meghan, his mother, is 50% Fey and 50% human, and Ash, his father, is human.
Keirran possesses the ability to use Winter, Summer, and Iron glamours. He has long, bright, silver hair and icy blue eyes. He is an excellent swordsman. He is also in love with a former summer court girl, Annwyl, who was banished by Queen Titania when she saw her a threat.
Keirran never meets his uncle Ethan, because Meghan had seen a vision in the Iron Prophecy that Keirran was to kill Ethan and that that would result in the beginning of a full war between all the courts and would cause the end. Fearing this, Meghan keep Ethan and Keirran as far away from each other as posible.
Despite this, Ethan and Keirran finally meet in The Lost Prince. Keirran helps Ethan escape from Meghan's palace when Ethan is being held there against his will, but he doesn't reveal he is Ethan's nephew untill Leanensidhe, Queen of the Exiles reveals it to Ethan. Puck remarks to Ash that both remind him of another pair, implying that Ethan and Keirran are very similar to Ash and Puck.