The mystery man is none other than Lee Gyul, a singer-songwriter who was also the vocal trainer for SISTAR's Hyorin and Soyu, Na Yoon Kwon, Nam Gyu Ri, and more.

Nam Gyu Ri unveiled on her Twitter, "Surprise~!! It's Lee Gyul who is singing a duet song with me this time. The album will be released on the 28th^^! Please look forward to it.! Anticipate, anticipate what kind of music will come out", along with snapshots showing the face of the man, which was kept hidden in her tweets yesterday.

Nam Gyu Ri is multi-tasking as a singer with her upcoming song release and as an actress starring in the new JTBC drama, 'Heartless City'.

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