Xenia, who is a very famous singer and songwriter, gets invited onto the set of family outing (back in season 1, which aired in 2008, so Xenia is 18 years old). She wanted to surprise Daesung, with her being the special guest. He didn’t know she would appear on the show. Only some of the other casting members know about Xenia and Daesung’s relationship, but know they can’t reveal it to the public, that however doesn’t stop their teasing completely.