Hoverlab, a South Korean news commentary site on YouTube, claimed that the actor and the late actress Kim Sae-ron had been in a six-year relationship since she was 15 years old.

According to Goldmedalist – an agency established by Kim Soo-hyun and his cousin – the actors dated from the summer of 2019, after she became an adult, to the autumn of 2020. Kim Sae-ron was born in July 2000, while Kim Soo-hyun was born in February 1988.

According to the actor's agency's statement, Kim Sae-ron was 19 at the start of the relationship and Kim Soo-hyun was 31.