MAMAMOO Solar and Kassy released their new collaboration song.

Solar and Kassy posted a jacket image of the collaboration song "A Song from the Past" on their official SNS at midnight on Jan. 13, respectively, to announce the surprise new song.

Solar and Kassy in the released photos attract attention with their clean-cut visuals and dimly-looking moods. 

The classical and elegant atmosphere of the two’s retro style stimulates curiosity about the collaboration song "A Song from the Past."

Before the release, attention was being paid to what musical synergies the Solar's delicate but explosive singing ability and Kassy's emotional warm voice will show.

As such, the unexpected combination of Solar and Kassy has already drawn enthusiastic responses from the risers.

The collaboration song "A Song from the Past" by Solar and Kassy was first released on various music sites at 6 p.m. on Jan. 16.