Thunder talked about a nerve-racking moment he experienced while filming the music video for his new solo track "Sign". 

During the press conference for his first solo mini album, Thunder revealed, "My older sister (Dara) played the most important role in my MV. She said she wanted to help me."

He continued, "There was a kiss in the scene where my sister appears. How could I have skinship in front of a family member? I didn't think it was right, so it was hard. I filmed it while shivering." 

You can check out the full MV of Thunder's "Sign" on December 7.