Terra is actually Xehanort. In KH2FM there is a secret video that shows a character (Xehanort) wearing the Org13 coat. He walks into Hollow Bastion/Radiant Garden and into a hidden room. In this room, the character sits in a chair and says,"Its been a long time...old friend."Then it shows Aqua's broken armor and her keyblade (i typed in Aqua's keyblade on google images).
The character sounds exactly like Xehanort. Plus in the hidden trailer, Terra's eyes glow yellow. In another trailer the Old Man is shown in a close up, his eyes start to glow red.
