Board Thread:Naruto Discussions/@comment-1512913-20160606161440/@comment-1512913-20160607092729

Unless she was a self-proclaimed princess, then there's only 2 ways she could have attained princesshood, being daughter of king/queen or wife of a prince.

If she was already a princess before coming to Earth, that would mean that there are Otsutsuki ranking above Kaguya somewhere out there.