He is King Gwangjong S01 E09

IU (as Go Hajin / Lady Hae Soo) Lee Joon-gi (as Wang So (4th Prince)) Kang Ha-neul (as Wang Wook (8th Prince)) Hong Jong-hyun (as Wang Yo (3rd Prince)) Baekhyun (as Wang Eun (10th Prince)) Nam Joo-hyuk (as Wang Baeka (13th Prince)) Kim Ji-soo (as Wang Jeong (14th Prince)) Yoon Sun-woo (as Wang Won (9th Prince)) Kim San-ho (as Wang Mu (Crown Prince / 1st Prince)) Seohyun (as Princess Woohee) Kang Han-na (as Princess Hwangbo Yeonhwa / Queen Daemok) Jin Ki-joo (as Chaeryeong) Z.Hera (as Park Soondeok) Sung Dong-il (as General Park Soogyeong) Kim Sung-kyun (as Choi Jimong / Homeless Man) Jo Min-ki (as King Taejo) Kim Kang-il (as Shincheon Kang) Park Ji-young (as Queen Yoo / Queen Shinmyeong) Park Jeong-hak (as Wang Shikryeom) Woo Hee-jin (as Court Lady Oh Sooyeon) Park Si-eun (as Lady Hae Myeong) Jung Kyung-soon (as Queen Hwangbo / Queen Shinjeong) Choi Byung-mo (as Park Younggyu) Lee Ho-jung (as Aera)

love triangle based on novel or book obsession forbidden love palace time travel royal family politics rivalry romance royalty family relationships tragedy historical fiction king period drama death tearjerker medieval power struggle historical drama reverse harem mother son relationship korean history brother brother relationship goryeo dynasty court intrigue