"Monstrum," an upcoming Korean monster action flick, started from a brief record in the Annals of the Joseon Dynasty that a strange monster haunted the royal palace in 1527 during the reign of King Jungjong. The king ordered his men to hunt it down but to no avail, said the historical record.

"The film features an imaginary creature. We made the monster based on our own imagination," Heo Jong-ho, who directed the movie, said during a promotional press conference at a Seoul theater on Thursday. "But if there's any difference, we got an idea from historical records."

The Annals of the Joseon Dynasty is a chronicle of the Joseon Dynasty (1392-1910) that covers the reigns of 25 kings during 472 years of history.

Jung Tae-won, CEO of Taewon Entertainment, which produced the film, said that he came up with the idea of cinematizing the story upon hearing that someone was writing a novel inspired by the incident recorded in the annals.

"A few years ago, I heard a story during a meeting with my acquaintances that there is a writer who is working on a novel based on the story that King Jungjong even moved his palace because of the monster. I thought it could not be a true story at first. But after confirming this from the Annals of the Joseon Dynasty, I thought it could be a really good idea for a movie," he said.

The producer then did everything to meet the writer and succeeded in persuading him to sign up with his studio to adapt his story into a film.

"Since there has been no quality Korean-style creature flick after 'The Host,' I thought the design of the monster should be very important for this film," Jung said. So, it took a very long time for him and director Heo to design the monster based on the description in the annals and their own imaginations. The result was a mysterious animal that looks like "haetae," a mythical creature known for symbolizing justice and prevention of fires and disasters in Korea.

"We're now considerably content with the design," he added.

Veteran actor Kim Myung-min plays the lead character of Yoon Gyeom, the king's loyal subject who goes after a monster endangering the monarch as well as a faction intent on removing him from the throne. Kim In-kwon plays Yoon's right-hand man, Seong-han, on the search team. The movie also has singer-actor Hyeri from popualr K-pop group Girls' Day and actor Choi Woo-sik as Yoon's curious and fearless daughter, Myeong, and a military officer who visits Yoon to deliver the king's order, respectively.

"The script was interesting and unique. The fact that I have to fight against an invisible opponent intrigued me. Also interesting was that the movie is based both on fiction and a true story," said Kim Myung-min. "I could see all the characters that I have since played in historical dramas in Yoon. There was something in common with what I played before, and I was drawn to the character which is neither too light nor heavy."

This will be the first appearance on the silver screen by Hyeri.

"I felt the movie's feature as a creature feature set in Joseon Dynasty was very attractive. It was an honor to work with such good actors who are senior to me."

She said her first-ever action made her nervous at first but she ultimately enjoyed filming it and learning how to shoot an arrow.

The Lotte Entertainment release is set to open in theaters on Sept. 13. (Yonhap)