The son of Yi In’s older brother, Grand Prince Munseong, played by Choi Ye-chan, is seen as a threat to Yi In’s reign in Captivating the King.
Yi In’s older brother, the former king, had to choose his successor between his own son, Prince Munseong, who was born while Yi In was the Qing’s hostage, and Yi In.
The King’s ill health gave rise to a succession crisis and a power struggle between the Queen and the Queen Dowager’s families.
Eventually, as the Queen Dowager’s faction wanted, Yi In ascended the throne, despite his brother’s wish for his son to inherit it.
Although Yi In becomes the King, some believe that he is a usurper who seized the throne from its rightful heir, Grand Prince Munseong.
To ensure that power remains in the hands of their family, the Queen Dowager and her brother, the Principal Director, have plans to assassinate Munseong.
On the other hand, Hee-soo and her group seek to dethrone Yi In and make Munseong, the legitimate heir, the King.
A worthy heir
When Yi In became the King instead of Munseong, he, along with Princess Jangryeong, protected Munseong from harm.
While the others consider Yi In a threat to the Grand Prince, Munseong himself is not scared of him, confident that Yi In would never hurt him.
Yi In’s wife, the Queen, sees him as a son, and Munseong loves her just as much. For her sake, he lies to the King about requesting the Gidaeryeong to teach him baduk.
He does wish to learn baduk because he wants to play with Yi In someday and hear stories about his father, whom he does not remember.
Although he is still too young, Munseong cares deeply about his nation as well as the people who are close to him.
He only agrees to the plan to substitute his sister with one of her court maids when he is assured that it would benefit the nation as well.
His involvement in the plot could have been considered treason, but Yi In forgives him. He takes it as an opportunity to teach him a lesson, but not without kindness.
Becoming the Crown Prince
After the substitution, Princess Jangryeong gets sent to a secure location, which means that she can no longer protect her brother.
This puts Munseong’s life in greater danger than ever before. However, Hee-so takes it upon herself to get Yi In to appoint Munseong as the Crown Prince.
She advises the sick Queen that this is the only way to ensure Munseong’s safety, leading to the Queen asking for her father’s help to petition the King.
Yi In agrees to honor the Queen’s last wish, as he wants the same thing. He promises to adopt Munseong and appoint him as the Crown Prince.
The King’s decision is opposed by the Queen Dowager and the Principal Director, who fear losing their power.
To placate them, Yi In claims that he will banish Munseong eventually, implying that Grand Prince Munseong is still not safe.
Also Read: Princess Jangryeong’s substitution in Captivating the King explained