Identity of Seo Kang-joon Revealed in Undercover High School

In the latest episode of MBC's Friday-Saturday drama Undercover High School (언더커버 하이스쿨), aired on March 14, the true identity of Jeong Hae-seong, played by Seo Kang-joon, was uncovered.

During the episode, Jeong Hae-seong and Oh Soo-ah (Jin Ki-joo) were deployed on a mission that ultimately failed. Upon hearing Oh Soo-ah's real name, Jeong Hae-seong realized she was his first love and stared at her in disbelief. He asked, "Is your name Bong-ja? Oh Bong-ja?" to which Oh Soo-ah replied, "Yes, that was my original name... But why are you laughing at someone else's name? It's rude to laugh in front of someone. I was going to take you home, but never mind. Go by yourself," before turning back into the store.

Reflecting on his childhood memories with Oh Soo-ah, Jeong Hae-seong's attitude towards her changed the next day. He arrived early at the teacher's office, gazing at her with affection as she danced, and complimented her, saying, "You’re amazing. You will definitely become a great teacher."

Meanwhile, Jeong Hae-seong and the members of the domestic team 4 gathered to find clues about a ghost story related to the school anthem. When they struggled with the piano performance, Oh Soo-ah stepped in, saying, "I’ll do it."

She insisted, "The school anthem itself isn’t that difficult," but Jeong Hae-seong warned, "You could get expelled for entering the chairman's office by mistake." However, Team Leader Ahn encouraged her, stating, "You can do it. You are the unparalleled partner of our National Intelligence Service's top ace, Jeong Hae-seong, and an honorary field agent of our domestic team 4."

Flattered by the title of 'honorary field agent,' Oh Soo-ah agreed to participate, despite Jeong Hae-seong's protests. She even requested a written agreement promising that the government would support her in becoming a teacher at Byeongmun High School.

Eventually, Jeong Hae-seong pulled her aside, firmly stating, "I won’t say this twice. Don’t do it. It’s dangerous." Oh Soo-ah responded, "All the teachers at Byeongmun High are attending the event anyway. Since we’ve decided to go together, let’s focus on the mission."

Jeong Hae-seong questioned her obsession with becoming a teacher, asking, "Why are you so fixated on it? You shouldn’t take risks just because it seems obvious. Be honest with me." Oh Soo-ah replied, "There’s someone I want to show this to. I promised my first student that I would definitely become a teacher. I’m determined to do whatever it takes to achieve that. Life isn’t worth living without risks."

As the operation approached, Jeong Hae-seong was conscious of Oh Soo-ah while teaching self-defense techniques. When she unexpectedly hugged him from behind during the lesson, he awkwardly excused himself, muttering, "Get a grip, you’re acting strange today."

At the highly anticipated Byeongmun Night, Jeong Hae-seong was captivated by Oh Soo-ah, who appeared in a dress. He reassured her, placing a camera necklace around her neck, saying, "I’ll make sure nothing happens today, so don’t worry. And by the way, you look beautiful today."

After successfully infiltrating the chairman's office, Jeong Hae-seong and Oh Soo-ah sat together at the piano to play the school anthem. When nothing happened, Oh Soo-ah expressed her confusion, saying, "Nothing is happening."

After the mission failed, Team Leader Ahn instructed Jeong Hae-seong to exit, warning, "Come out, Hae-seong. It’s dangerous to stay there. Erase the entry records from the chairman's office and get out quickly." Following the order, Jeong Hae-seong announced, "I will withdraw," as he deleted the entry records from Seo Myung-joo's (Kim Shin-rok) computer. In that moment, he discovered his personnel record card and the operation plan file for Byeongmun Night, leaving him in shock. The upcoming preview hinted at Jeong Hae-seong taking independent action with Oh Soo-ah, raising questions about the plot's development.