Singer Yoon Hyun Sang and IU's debut title song, "When would it be" teaser was released.

On October 29, Yoon Hyun Sang released the teaser of his title song on Facebok.

In the teaser, Yoon Hyun Sang and IU were in a fantasy-like world coming in and out of the fantasy and reality. Their mysterious and unique looks added to the curiosity and emotions that the two artists will bring out together.

LOEN Tree said, "Yoon Hyun Sang and IU's beautiful harmony and mysterious video made the video into a movie-like film. We hope for much support for his music."

The full version will be released on October 31.