South Korean director Jason Yu’s mystery thriller “Sleep” won the top Grand Prix award at the 31st Gerardmer Fantastic Film Festival in Gerardmer, France.

Yu’s win marks the first for a Korean film in 20 years, after Kim Jee-woon’s “A Tale of Two Sisters” won the prize in 2004.

“Sleep,” which opened in domestic theaters in September last year, is Yu's feature-length directorial debut. The late actor Lee Sun-kyun and Jung Yu-mi star as newlyweds who go through a hard time after Hyun-soo's (Lee) begins exhibiting strange behavior while sleeping. His pregnant wife Soo-jin (Jung) goes to desperate lengths to solve the problem.

The Gerardmer International Fantastic Film Festival, dedicated to the fantasy genre in all its forms including sci-fi, horror, supernatural and more, was established in 1994.

"Sleep" received favorable reviews from critics, attracting 1.47 million moviegoers in Korea and easily surpassing its breakeven point of 800,000. Before the local opening, the low-budget was also invited to the 76th Cannes International Film Festival’s Critics’ Week section in May last year, a rare feat for a new director.

Prior to debuting as a director, Yu worked with renowned directors for several years. Yu worked with Lee Chang-dong for “Burning” in creating English subtitles and Bong Joon-ho for “Okja” as a sound mixing coordinator. He also created two short films: “Video Message” in 2014 and “The Favor” in 2018.

"Sleep" is also the final work by Lee who died last month after a weekslong police investigation into allegations he had used illegal drugs.