Singer Sunmi's eyes were filled with tears at the appearance of her stepfather.

On December 7th, Mnet pre-released videos of 'Running Mates' before they air the first episode on December 9th. In the video, the members of the show were resting together in their dorm when a sudden known came from the front door.

After hearing the knock, Sunmi ran to the door and shouted, "Dad!" in surprise.

During the interview with the production team, Sunmi revealed that her dad was actually her stepdad.

Sunmi explained, "I spent time with my stepdad ever since my dad passed away. I've spent that much time with him. Even though we don't have a drop of blood mixed with him, he took care of us three siblings..." and couldn't finish her sentence as she began tearing. She continued to say, "There are so many things I'm thankful to our dad." 

In a broadcast aired in 2018, Sunmi confessed that her father died three months before her debut from pulmonary tuberculosis complications, expressing her family's difficult situation as a child.

Meanwhile, 'Running Mates' is a reality show that will premiere on Mnet at 7:50 PM on December 9th KST. Female idols in their 20s, representing K-pop, become one "running crew" and run in the nation's beautiful running course surrounded by mountains and the sea.