After promoting as SS501's vocalist for seven long years, Heo Young Saeng made his debut as a solo artist on today's episode of "M! Countdown" with his title track, "Let It Go"! Produced by Sweetune, the song describes the different ways men and women approach love, and the misunderstandings that result from it. Joining Young Saeng is 4minute's HyunA with a rap part expressing the inner feelings of women but it was Park Ju Hyun appearing on stage. This urban pop song has both a simple but strong beat with a combination of both ballad and dance and an upbeat chorus that brings out the best in Young Saeng's sweet voice. Check out his debut stage below!