• 'Train To Busan (Bu_San-Haeng)' Photocall - The 69th Annual Cannes Film Festival

'Train To Busan (Bu_San-Haeng)' Photocall - The 69th Annual Cannes Film Festival (Photo : Getty Images)

It is Sept. 19, Monday, and the 31st birthday of “Descendants of the Sun” actor Song Joong-ki. Beside the alleged secret relationship with and planned wedding proposal to Song Hye Kyo, another new speculation is swirling around the Hallyu star.

Mobile & Apps reported on Monday that Song Joong-ki could possibly be in "Train to Busan 2." As of Sept. 15, the original “Train to Busan” had grossed $99 million, prompting rumors of a sequel to the popular zombie apocalypse film.

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Lead star Gong Yoo has confirmed, through a tweet, a sequel to the movie, but what is still a big question mark are who would be the actors. Even Gong Yoo has expressed interest in returning to the sequel and told director Yeon Sang Ho of it, but the director told him his character, Suk Woo, is already dead after he jumped off the train and broke his neck.

“So then I recommended that the sequel is made from Ma Dong Seok’s point of view since Ma Dong Seok’s character is alive as a zombie.” The website added Gong Yoo has also approached the producers and could possibly reprise his role, but like the Song Joong-ki romance rumors, Mobile & Apps admitted all those tidbits are based on unconfirmed reports.

Movienewsguide also reported of the possibility of Song Joong-ki’s participation in the sequel, with him and Gong Yoo possibly playing zombies.

Sony Pictures and 20th Century Fox are said to be interested in making “Train to Busan 2.” Based on the credits of the original movie’s trailer, one of the producers of the movie is NEW, or Next Entertainment World,” which is producer of “Descendants of the Sun,’ so speculations about his possible inclusion in a sequel may not be farfetched, although Blossom Entertainment, the agency of Song Joong-ki, had previously stated the only commitment of the birthday boy is shooting “Battleship Island” until end of 2016.