On the 10th episode of KBS 2TV drama,"Big," Gong Yoo (Seo Yoon Jae) and Shin Won Ho (Kang Kyung Joon) find out their mother's are the same person.

On the July 3 episode of "Big," Lee Se Young sees Seo Yoon Jae's mother, Hye Jung, talking about Kang Kyung Joon, creating suspicion.

Se Young overhears Hye Jung's phone call and Kyung Joon runs a blood test.

The blood test revealed that Kyung Joon was Hye Jung's son. Se Young debates whether or not she should tell Yoon Jae this newfound truth.

Se Young goes to Kyung Joon's aunt, Kyung Mi and asks if Kyung Jun's mom is Hye Jung. His aunt says, "She is his real mom. Why are you asking me that? Is there something wrong?"

Se Young replies, "Nothing. I was just checking the patient's family history."

Se Young thinks to herself, "If the test results are true, then Yoon Jae's mom is Kyung Joon's mom too. Maybe his birth mom is different?"