The Wormhole wrote:
However, the stuff about "breaking the promise" implies to me that he probably is later incarnation that chose for some reason (Time War, perhaps?) not to call himself the Doctor.
I thought about that too, however, the Doctor refers to him as his big secret. But everyone knows the Doctor was involved in the Time War, and at least somewhat know what he did (he was the one who locked Gallifrey and the Daleks away, cutting the war off from the rest of time and essentially destroying them), so it's not much of a secret.