Trystane Martell

Trystane Martell is an unseen character in the second season. He is first mentioned in "What is Dead May Never Die".

Background
Trystane is a member of House Martell, the ruling house of Dorne.

Season 2
Trystane is proposed as a potential marriage candidate for Myrcella Baratheon by her uncle, Hand of the King Tyrion Lannister. The alliance with the Prince of Dorne is accepted and Myrcella is sent to Dorne.

In the books
In the Song of Ice and Fire novels, Trystane is the youngest son of Prince Doran Martell, the ruler of Dorne. He has olive skin and straight black hair. He is two years older than Myrcella Baratheon, making him about 12 years old when they are betrothed.

Trystane is the youngest child of Doran Martell, and thus not the heir to the rule of Dorne.