Previously, it was reported that Heechul's duet might be with none other than MAMAMOO's Whee In - and it turns out that this is right!

SM Entertainment released an official statement regarding the news on March 29 with, "It is indeed MAMAMOO's Whee In who will be in the duet with Super Junior's Heechul.  We plan to release it in April."

This is going to be amazing!  Whoot whoot!