Dean-Charles Chapman took over the role of Tommen Baratheon from Callum Wharry in Game of Thrones season 4 - but what was the reason for the casting change? The younger brother of Joffrey and Myrcella appeared as a background character in the first two seasons before his role expanded in season 4.
Tommen was said to be the son of Robert Baratheon and Cersei Lannister but that wasn't exactly the case. Like his two siblings, his true father was his uncle, Jaime Lannister. Prince Tommen was essentially a minor character in the first two seasons: he visited Winterfell with his family, was shown visibly upset when Myrcella was sent to Dorne, and was nearly poisoned by Cersei during the Battle of Blackwater. Tommen was weak-willed and often ridiculed by Joffrey, but that changed in season 4 when he took over as Lord of the Seven Kingdoms.
The role of Tommen marked Wharry's first acting gig. He was considered a guest star in season 1 before the young actor was asked to return for the following season. However, the character didn't appear in Game of Thrones season 3. When Tommen returned to the series in Game of Thrones season 4, he was portrayed by Chapman, a recast that came about thanks to multiple reasons.
The biggest was his increased role. After the death of Joffrey, Tommen was forced to wear the crown, becoming a key pawn in the conflict between Cersei and House Tyrell through to his death by suicide in season 6, Because of the new complexities of the role, the Game of Thrones writers wanted a more experienced actor to take control of Tommen's arc.
Chapman wasn't a stranger to the series when he was recast as Tommen in season 4. The actor portrayed Tommen's cousin, Martyn Lannister, in the third season. Martyn was killed that same season so, at the time, Chapman thought his Game of Thrones work had come to an end; Chapman wasn't cast as Martyn to with the intention of later filling in for Tommen.
But besides the demands of the role, Game of Thrones simply needed an older version of Tommen which is another reason why they had to recast the role. Chapman was 16 years old when he first portrayed Tommen, three years older than Wharry. Those few years made all the difference in convincing viewers that he was old enough to wear the crown and consider marrying Margaery Tyrell (something he did at 9 years old in the books, but the show aged up). Unlike the Game of Thrones series, Tommen is still alive in the novels and serves as a background character.