Although Seo In Guk has rarely shown off his body in the past, it seems the current The Master's Sun star has finally gained confidence in his physique -- and we can see why! The fact that he currently plays a bodyguard in The Master's Sun as well as a swimmer in the upcoming film No Breathing most likely played a role in his improved fitness.

Netizens replied with a positive response of "I think I had a heart attack!" and "Why isn't he working out in my neighborhood? T_T"

Check out Men's Health's September issue for more information on Seo In Guk's transformation.