SISTAR's Hyorin had good friend Park Seo Joon make a special appearance during her guest spot on 'Yoo Hee Yeol's Sketchbook'!  The two had acted together in the past and had stayed close since.

She first talked about her first new solo album in three years, revealing she participated in the whole production process, from choosing the concept to the outfits.  She admitted, "It was so hard I wanted to give up.  I felt like I was going to cry when the album was released, but the tears didn't actually come when I got [the album]."

She revealed the song she was most attached to out of the other tracks on her album was "Slow."  Then, the actor appeared on stage.  She said, "Park Seo Joon thinks of me as a man."  Park Seo Joon simply said, "I don't see you as a woman," making everyone laugh.

SEE ALSO: First court hearing scheduled for former NCT member Taeil's quasi-rape case

They revealed that they would talk to each other about their problems.  Hyorin said, "Park Seo Joon is the 'chindeure' style (someone who seems cold and distant on the outside but is secretly caring on the inside).  He just grunts in front of you, but he takes care of you behind your back."

Park Seo Joon said, "I first saw SISTAR in the military," revealing he likes their song "Crying" the best.  The two were told to express each other with just one word.  She called him "lighthouse" while he called her "diva."