The singer-turned-actor was spotted showing off his newly defined V-line and a hint of his muscular build, which he achieved through intense weight training for his role as the security guard Kang Woo. 

Seo In Guk's agency, Jellyfish Entertainment, stated, "Seo In Guk is putting his all into his expressions for his role as Kang Woo. Following his casting for the drama, he also worked hard to achieve a great figure through dieting and weight training to complete Kang Woo's character, who is known for his superior visuals."

You can catch more of Seo In Guk on 'The Sun of My Master', which is premiering after the finale of 'I Hear Your Voice' on the 31st at 10PM KST!

SEE ALSO: So Ji Sub, Gong Hyo Jin, Seo In Guk, and more attend first script reading for 'The Sun of My Master'