SEE ALSO: DJ Koo Jun Yup reportedly lost 12 kg (26.4 lbs) after losing his wife Barbie Hsu

One of the most memorable moments from filming occurred when Donghae said to Eunhyuk, "Ack, you're ugly," to which Eunhyuk replied, "Because you keep making fun of my face, my mom dislikes you," causing laughter among the staff members.

As 'Wonderful Day' follows the Super Junior members on their once-in-a-lifetime trip to Switzerland, Donghae and Eunhyuk continued to bicker throughout the whole vacation. They said things like, "I'm getting stressed. My head hurts. Be quiet," to each other, pretending to get annoyed with each other.

At one point however, Donghae spoke his true feelings regarding his friendship with Eunhyuk in an interview, saying, "Even so, thank you for always letting me tease you. Even in the future, I want to always be happy like this together with you."