In "Cantabile Tomorrow" Joo Won subtly showed that he was jealous of Shim Eun Kyung.

On the episode of KBS 2TV Monday/Tuesday "Cantabile Tomorrow" broadcast on November 11th, Cha Yoo Jin (played by Joo Won) and Lee Yoon Hoo (played by Park Bo Gum) got into a love triangle. They were both into Sul Nae Il (played by Shim Eun Kyung) and subtly expressed their feelings for her.

The two people started to put their guards up as they ran into Sul Nae Il in front of Yoo Il Rak (played by Go Gung Pyo)'s store. Afterwards, until they parted ways, they did not let go of their tension and thus attracted the attention of the audience.

After Lee Yoon Hoo went home first, Cha Yoo Jin said, "It's kind of confusing so you better be straight. If the two people fight, who's side are you going to take?" and showed his jealous in front of Sul Nae Il.

Hearing this, Sul Nae Il was embarrassed and smiled, saying, "I'm always on your side. I'm always on Yoo Jin's side."

Meanwhile, "Cantabile Tomorrow" is a KBS2 Monday/Tuesday drama adapted from the Japanese manga with the same title. In the drama, Yoo Jin (played by Joo Won) is a piano major with a world famous pianist father who is not only attractive but has exceptional music talent.