Crimson Moon (2015)

Crown Prince Sado gets sent to Jeoseungjeon where Gyeongjong the Great and Jang Huibin used to reside due to his father Yeongjo's political ambition. One day, a dead body of an eunuch gets thrown in Crown Prince Sado's room. Crown Prince Sado and Princess Hwawan try to find the culprit but things get more mysterious. Meanwhile, in the middle of the night, the mother of Crown Prince Sado visits Jeoseungjeon to check on his son and happens to witness a big secret.