Trystane Martell

Youngest of Doran's three children, betrothed in his cradle and again in his boyhood to Princess Myrcella Baratheon under the Lannister peace. By A Feast for Crows the pair are companions of a sort at the Water Gardens, playing at cyvasse on shaded marble while their fathers' realms grind toward war. The night Ser Arys Oakheart died on Arianne's command, Trystane was kept clear of the blood; he goes on quietly afterward in the Water Gardens at his father's pleasure, an heir-in-reserve no one yet treats as one.