Baek Sung-hyun

Chae Woo-ri

King Mokjong of Goryeo

Kim Jong-hyun: Seong-ok's college senior who is a jewelry brand designer.

Jang Kyung-joon

Pi Young-gook – Neurosurgery's 3rd year resident doctor and Seo-woo's friend who had a long-time crush on her.

27-year-old Park Hyun-soo

Crown Prince Sohyeon Shin Ki-joon as child Crown Prince Sohyeon

Jang Dae-seok (ep. 1-2, 9-10)

Park Hyun-woo

Kang Byung-jin

Adult Choi Jung-woo

Gil Choong-shik, Da-ran's brother

Crown Prince Uigyeong (1–23) & Seongjong of Joseon (40–54) (dual role)

Park Mu-yeol, an honor student who is driven by morals and justice.

Han Sang-chul (Ji-soo's younger brother) Cha Jun-hwan as young Sang-chul

Young Gungbok

Young Song-joo

Young Yoon

Young Jun-ki

Young Lee Min-chul