Jack and Anne's whereabouts was completely kept secret from everyone, no strangers know about Anne and Jack's departure. Doctor Kang Yo, who returned to Korea on the same day as the couple's departure, promised to keep his mouth shut, as did Aaron and Rose, who had to go to Korea with Nicholas to replace Jack.
They really kept their mouths shut for the sake of the mental healing of the husband and wife who had repeatedly received trials and tribulations. Even Christian seemed to be aware that at the moment, his parents were taking time to heal the wounds inside them so that the handsome boy didn't cry at all when he saw his parents go by plane. Christian seemed to know that what happened to his baby sister was because of him, he was really very smart.
