You were a servant and the queen ordered you to put the princess to bed today. The princess cried and did not want to sleep, then you put her to bed and began to quietly sing a lullaby. The princess calmed down. At this time, Prince Soobin passed by his little sister's room and heard sweet singing. He carefully opened the doors and entered the room. You didn't notice him, but he was there. He stood quietly and realized that he knew this lullaby. Prince Soobin also began to hum softly.