"Respond 1997" Seo In Guk told everyone that he was Jung Eunji's boyfriend.

On the Tuesday episode of "Respond 1997," Yoon Jae, in front of other people, said that he was indeed Si Won's boyfriend.

Yoon Jae was appearing on a TV program, of which Si Won is a crew member. He was meeting with an anchor, producer and a writer before the show. The anchor tried to hook her arm around Yoon Jae and said that she'd like to have a private conversation with him in the waiting room. However, he removed her arm and this made Si Won laugh.

Then unexpectedly, he took the coffee that Si Won was drinking and put it in his mouth. 

The producer remarked that the two of them seemed close, to which Si Won agrees. Yoon Jae, then seriously, says "I'm her boyfriend." While everyone is shocked, he says, "I'm not interested in teenagers. Just her." 

After that Yoon Jae and Si Won leave arm in arm, leaving the anchor fuming.