Lee Jung-hyun, one of the stars of the upcoming flick “The Battleship Island,” knew her co-star Song Joong-ki was going to marry Song Hye-kyo before the couple made it public. “I actually knew about their marriage beforehand, but I couldn’t tell anyone else,” she said during a joint press interview Tuesday.The so-called Song-Song couple announced earlier in the month that they would wed on Oct. 31, after repeatedly denying dating rumors. The singer-turned-actress said she jokingly offered to sing her hit “Bakkwo” -- which means change -- at the wedding. However, the couple asked singer and musical actress Ock Joo-hyun to sing instead. Lee and Song Joong-ki star in “Battleship Island,” which will hit theaters Wednesday. The film is about forced Korean labor by the Japanese during World War II.()