100 Days My Prince (Korean: 백일의 낭군님; Hanja: 百日의 郎君님; RR: Baegirui Nanggunnim; lit. Hundred-Day Husband) is a 2018 South Korean television series starring Do Kyung-soo and Nam Ji-hyun. The series aired on tvN from September 10 to October 30, 2018, every Monday and Tuesday at 21:30 (KST). It is the eleventh highest-rated Korean drama in cable television.
Lee Yul is the king’s nephew who enjoys spending his days playing instead of studying. He enjoys playing with the peasant children alongside his best friend and guardian, Dong-joo. One day, as he is playing with the peasant children where they play the villains, Yul uses his status to punish the children by beating them up, oblivious that his actions are hurting them. The children could not object to this treatment due to Yul’s status. A girl, Yoon Yi-seo intervenes and chides Yul for his cruel actions. Like Yul, Yi-seo is from a noble family, but is kind, smart and compassionate. Yul instantly develops a crush on Yi-seo, and this causes him to change to become more studious in order to impress her. Yi-seo’s father is a general and the right-hand man of the king.
However, Yul’s father is an ambitious man who is jealous of his brother, the king, and vies for the throne. Scheming with another ambitious man, Kim Cha-eon, they plot to overthrow the current king, with the promise that Cha-eon will be handsomely rewarded. One night, Kim Cha-eon begins the coup which sees the king and all his men and allies ruthlessly murdered, including Yi-seo’s father. While fatally injured, Yi-seo’s father instructs his elder son Seok-ha to take Yi-seo and run away, as Cha-eon is determined to wipe out the entire family. As Cha-eon is about to deal the killing blow, Yul, who has been witnessing the whole thing, comes out from his hiding to stop Cha-eon, threatening that he will report this matter to his father. Cha-eon then carries Yul back to his father’ mansion and it is then made known that he has been conspiring with Cha-eon for the whole thing all along, shocking Yul. Yul is removed from the scene and the coup is completed successfully. Due to this, Yul’s father is crowned as the new king and Cha-eon becomes the vice-premier. Yul automatically assumes the title of Crown Prince, and is further shocked on the coronation day with the news of his mother’s “accidental death”. Despite the new king’s surprise at the news, it becomes clear that the vice-premier will be the person who has the most power and control of the new reign. Yul bitterly resents his new position as the Crown Prince of Joseon.
Sixteen years later, Yul has grown up to be a cold and unlikable crown prince. Due to the trauma of his past, Yul is also very smart and skilled in the martial arts. His father is now remarried to the new queen who dislikes him and wants the Crown Prince title for her own son while he himself is married to Kim So-hye, who is Vice-premier Kim’s daughter. Despite the marriage, Yul still longs for Yi-seo, even though he believes that Yi-seo was killed. This causes him to despise the crown princess and her father and his constant avoidance of consummating the marriage, despite the various schemes in place to ensure the consummation takes place. At the same time, a drought happens in Joseon and people begin to blame Yul and his refusal to consummate the marriage as the reason. Annoyed, Yul orders all the singles in the nation to be married off in a month to help alleviate the drought.
While en route to a rain ritual, Yul and his followers are ambushed by assassins arranged by Cha-eon, and he is almost killed. The crown princess was pregnant with another’s child (later revealed to be Mu Yeon’s, Hong-shim/Yi-Seo’s brother) and the crown prince’s assassination attempt was to escape from her predicament. His childhood friend and guardian, Dong-joo, forces them to switch their garments, essentially luring the attackers away from Yul. Dong-joo is subsequently killed and falls into the river, the attackers did not get to see his face and thus believed that it is Yul. Meanwhile, Yul gets shot with an arrow on his chest while on the run, and accidentally knocks his head, becoming unconscious. When he wakes up, he has already lost his memory.
Yi-seo, who managed to escape unscathed in the coup years ago, has been adopted by a commoner man and now lives undercover as a peasant girl named Hong-shim in Songjoo Village. It is her adoptive father who found the terribly wounded Yul and nurses him back to consciousness. The fate of her brother Seok-ha is unknown, as they separated after Seok-ha buried her under a stack of leaves and ran away to lure Cha-eon’s people who were hunting them in the woods. Before separating, they promised to wait for each other at a bridge every 15th of the month. While Yi-seo goes to the bridge as promised without fail, it has been sixteen years since the separation and she is beginning to lose hope that her brother is still alive.
As a single woman, Hong-shim is also subjected to the crown prince’s marriage decree and she happens to be the oldest single woman in the village. Due to the imbalance number of single men and women, Hong-shim finds herself the only one without a pair. Instead, she receives an offer to become the concubine of a lecherous nobleman. Hong-shim refuses because she says that she is already betrothed to a man named Won-deuk who is serving in the military and has no intention of being the man’s fifth wife. The deadline for the decree passes by and since Hong-shim is still unmarried, she is subjected to the punishment of 100 floggings. To save her, her father takes advantage of Yul’s amnesia. A very skeptical Yul is told that he is Hong-shim’s betrothed, Won-deuk, a man whom her father had recommended but whom she had never met.
Thus, Yi-seo and Yul get married while neither of them are aware of each other’s true identities. The rest of the story follows how the prince seems very strange to the commoner’s lifestyle and is initially considered a good-for-nothing-husband by the villagers. However, his skills of reading, writing and martial arts remain which impresses Hong-shim and the villagers. He eventually returns to the palace and regains his memories of Yi-seo later and the two reunite again.