It isn't even a proper name; his real name is lost in the darkest recesses of his mind, forgotten by everyone, including himself. He has so many nicknames, but nobody could ever really call him anything that worked, that made such perfect sense that he knew without a doubt that that was who he was.
Except for her.
My Doctor, she had called him, and in that moment the ancient scars in his hearts healed.
But now they've been torn open and bleed anew, because the puzzle of his universe is missing that one last piece.