Actress Nell Tiger Free took over the role of Mrycella Baratheon from Aimee Richardson in Game of Thrones season 5 - but what was the reason for the recast? Cersei Lannister's only daughter appeared in the show's first two seasons but her story arc didn't become important until the fifth.
Myrcella was thought to be the daughter of Cersei and Robert Baratheon but her father was actually uncle Jaime Lannister, as was the situation with her two brothers. During the first few seasons, Myrcella was a minor character as the middle Lannister child growing up in King's Landing. In season 2, Tyrion struck up a political move that would unite the Lannisters with House Martell. As part of the alliance, Myrcella was sent to Dorne to eventually wed Trystane Martell. By the time the character reappeared in Game of Thrones season 5, another actress was playing the part.
Richardson played Myrcella in the Game of Thrones pilot episode but at the time, it was a non-speaking role. She was considered a stand-in as the character was not officially cast yet. The actress made an impression because she was later cast in the role proper for the rest of season 1. She returned for the show's second season and played Myrcella when the character was shipped off to Dorne. Myrcella didn't appear in the third and fourth seasons but her name was mentioned. By the time she returned in season 5, Free was in the role and there has been no real explanation surrounding the recasting.
Throughout the series, Richardson appeared in a total of eight episodes. She, along with the viewers, learned about the recasting during a San Diego Comic-Con panel ahead of the fifth season. The actress hilariously responded by holding a sign indicating that she was available for hire as the news took her by surprise.
Since Myrcella became a key figure in the conflict between the Lannisters and the Martells in season 5, it seems likely that they wanted an actress who could expand the role. Richardson is actually older than Free so age concerns with a maturing character didn't seem to be the case. It wasn't uncommon for Game of Thrones to recast roles without giving a solid explanation, such as with the Night King.
Free portrayed the character in Game of Thrones season 5 and 6 but in reality, she played the part in only four episodes. Even though she was only in a small handful of episodes, they were integral to the plot. As an act of revenge for Oberyn's death, Ellaria Sand set her sights on the innocent Myrcella. Before she allowed the young girl to leave with Jaime, Ellaria gave her a quick kiss but her lips were coated with poison. Myrcella died from the poison before making it home and only her lifeless body was shown in the sixth season. Her death gave Cersei a new direct enemy in Ellaria and it wasn't long before she fought back.