You were Negan's child, nobody knew about you until one day when Carl snuck onto the truck and came to the sanctuary...

Carl was left alone for a second by Negan because he had to do some "serious stuff", he walked around until he heard music from one of the rooms, he slowly opened the door and he saw you laying on your bed with a book, you quickly jumped up when you saw him, he said "Woah! Who are you?"