Shin Dong Yup surprised everyone with a slightly dirty joke.

On Saturday's episode of KBS "Immortal Song 2," singers Lee Sang Eun and Lee Sang Woo appeared as the legends to be featured. INFINITE's Sunggyu sang Lee Sang Eun's "Dam Da Dee."

Sunggyu defeated Ailee in a first round battle and now he was facing off against Sonya. He said, "When this song was first released, I was still in my mom's belly. It's such a famous song that I've known it since before."

When Sunggyu was facing the judges, Shin Dong Yup asked him if he was born when the song came out, to which Sunggyu replied that he was still in his mother's womb. Then Shin said, "No, the song came out in the summer so you can't be sure that you were on your mother's side."

When everyone released the slightly dirty nature of the joke, it sent the performers and the judges laughing.