Joo Sang-wook

Han Sang-jin: Soo-hyuk's best friend and business partner who is the representative of the book publishing house Jinri.

Jang Gang

Yi Bang-won, King Taejong, the 3rd King of Joseon. Known as "Duke Jeongan" (정안공; 靖安公).

Cha Jung-Hyuk, a beauty representative and makeup artist.

Kang Min-ho (ep. 2)

Tae In-joon Choi Seung-hoon as young In-joon

Lee Kang, Prince Jin Yang (King Sejo) Choi Kwon-soo as young Lee Kang

Ryu Hae-sung

Jin Hyeong-woo Nam Joo-hyuk as young Jin Hyeong-woo

Ha Dae-chul Noh Young-hak as young Ha Dae-chul

Han Tae-hee

Cha Jung-woo

Joo-yeon's 2nd ex-boyfriend (cameo, ep. 1)

Kim Do-han

Choi Jae-ha

Seo Yoon-ho

Hyun-woo (cameo, episode 9)

Lee Young-jo Lee Tae-ri as young Lee Young-jo

Jo Min-woo Noh Young-hak as young Min-woo

Kim Kang-mo (Ji-soo's secret boyfriend)

Wolya

Lee Joo-hyuk

Jung Chan-young

Park Jae-woo

Ahn Kang-hyun