After sitting down for a break from working. A thought sparked in my mind. Remember when Xemnas walks down in the room of sleep he sits down and looks at Auqa's armor and says "hello old friend" or something on those lines. Well what I had realized is that is almost indesputible evidence that Terra is most likely Xehanort. The reason is that well obviously the three knights are some what being like Sora, Kairi, and Riku. Riku in KH1 fell to the darkness Maleficent hand consumed him in. And Riku is most connected to Terra. Well evidently we see Terra talking to Maleficent which would also spark why when he is working for Ansem he has a intrest in the darkness of the heart. Being with Maleficent he could learn her ways and cunningness of persuading people. Giving him the ability to get all of Ansems assistants to follow him. Therfore back to my first point why Terra is Xehanort Xemnas would have memories of his"past" life. So saying to aqua "friend" would signal a key indicator that he was Terra a while back. Comment if yah like. Remember this is all speculation so don't bash me if you don't like my theory.
