SEE ALSO: Kang Ji Yong, Kwon Eun Bi's cousin and recent 'Divorce Camp' cast member, dies at 36

'Roommate' PD Park Sang Hyuk told Star News on the 29th, "Lee Soon Jae was invited to the 'Roommate' share house... The members were surprised at the arrival of the veteran sunbae."

It turns out Sunny and Bae Jong Ok were the ones who invited Lee Soon Jae to the share house. Sunny had kept in touch with him as she was previously on 'Grandpas Over Flowers', while Bae Jong Ok is his acting hoobae.

The PD added, "The two of them went to watch Lee Soon Jae's play 'On Golden Pond' and as they were talking in the waiting room, they asked him to have a meal at their house... The producers weren't aware of it and the members were also not expecting it so they were very surprised."

Lee Soon Jae's appearance will be aired through the episode this Sunday at 4:50 PM KST!