Just like the title says I found a spoiler or rumor in the plot but because we have to wait like how shall I say another four years you might want to take a look at this story and read it carefully.
http://kingdomhearts.rpgplanet.gamespy.com/kingdomhearts3/story.shtml
http://kingdomhearts.rpgplanet.gamespy.com/kingdomhearts3/story.shtml