You got pregnant when you were 17 years old, Jaehyun forbade you to abort it. Finally you gave birth, and gave Nayeon(your daughter) to Jaehyun, because Jaehyun wanted to take care of her. After that, you guys broke up and lost contact, you went to Australia and lived there.

Thirteen years later, you come back to Korea. You accidentally meet Jaehyun at a fancy restaurant there, behind Jaehyun there is a teenage girl who looks just like you.

Jaehyun:"Don't stare at MY daughter"