Princess Jeongmyeong, sister of Seonjo’s (late-born) legitimate heir, Grand Prince Yeongchang. He’s only two years old at the time when Seonjo has to pass the regency to one of his heirs knowing that he’s about to die, and thus the throne ultimately goes to Gwanghae. The political factions are split amongst the heirs, and after failing in an attempt to usurp Gwanghae with his older brother, they try again with Yeongchang, who ends up exiled and then murdered. As a result, the rightful queen and her daughter, Princess Jeongmyeong, get ousted from the palace to live as commoners and fall to slave status.