Previously, singer Heejun revealed that he'd be working with a Girls' Generationmember for a special duet!  

However, he did not reveal the identity, just dropping hints to agonize fans who made guess after guess.  Now the Girls' Generaiton member is revealed to be none other than "twinkling" member Tiffany!

SM Entertainment confirmed this with OSEN today, saying, "The singer collaborating with Heejun is Tiffany."

Their duet track will be out on May 15!