"She had all of her mother's beauty, and none of her nature."
Tyrion thoughts on Myrcella.

Princess Myrcella Baratheon is a member of House Baratheon of King's Landing and a member of the Baratheon royal family. Myrcella is the second child of Jaime and Cersei Lannister, although officially of Robert and Cersei, and their only daughter. Myrcella lived in King's Landing through to Joffrey's reign, when Tyrion arranged for her to be married to Trystane Martell to secure the allegiance of Dorne, although Cersei tried to stop it. Myrcella spent several years living in Sunspear getting to know Trystane, under the protection of Ser Arys Oakheart of the Kingsguard. In the show, Ser Jaime and Bronn try to rescue her when the Sand Snakes make an attempt on her life. While Jaime arranges for Myrcella to be taken to King's Landing to marry Trystane in safety, Ellaria coats her lips with poison and kisses Myrcella goodbye, where she later dies on the ship. In the books, the Sand Snakes instead try to steal Myrcella away from Doran Martell, hoping to crown Myrcella as queen following Joffrey's death