SM Entertainment duo M&D has announced a comeback.

M&D, a project group made up of Super Junior’s Kim Heechul and TRAX’s Kim Jungmo, will be releasing music for the first time in four years. The duo released a song last in 2011, prior to both Jungmo and Heechul enlisting in the Korean Army to fulfill their obligatory military service. SM Entertainment has not released an official statementabout the comeback, but both Heechul and Jungmo mentioned the comeback on their Instagram accounts.

On January 27, Jungmo shared a picture of himself sitting in front of a computer, editing music. The comment on the picture was “Coming soon!!! #MnD,” without any timeline for the upcoming release.

It is unknown whether M&D’s name will be stylized as MnD for this comeback, although Heechul used the same tag in a video uploaded the same day. He also included the word “Soul,” which is likely the song title.

Jungmo previously shared a photo of the two of them in the recording studio in November.