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

On Feb. 16, 2025, Korean actress Kim Sae Ron was found dead at home. The death of the 24-year-old, who had risen to popularity as a child actress, was later ruled a suicide. Reports soon began to emerge that Sae Ron had owed 700 million won (S$652,000) to her former agency, Gold Medalist, at the time of her death.