Kingdom Hearts 3 Trailer Confirms Second Playable Character

Since Tetsuya Nomura hinted about the possibility years ago, fans have speculated about whether Kingdom Hearts 3 will have another playable character beyond Sora. Now, the sequel's latest trailer has confirmed that is the case, and who this second character is.
Spoilers for Kingdom Hearts 3 follow! Turn back if you haven't watched the latest trailer for the game and don't want to know.
During the Kingdom Hearts 3 Final Battle trailer, viewable above, gameplay of Riku as a player-controlled chara