“But not in the name of the Doctor!”
— The Doctor and… the Doctor?
At last, the Doctor’s greatest secret is revealed. Not his name, or the reason he left Gallifrey — but rather that he has been hiding an entire persona, apparently even from himself.
That never-before-seen face (John Hurt’s face, to be precise) was hidden way down deep at the bottom of the Doctor’s mind, and now Clara knows about it. The reveal of a previously unknown incarnation of the Doctor has shattering repercussions — only the very least being the potential renumbering of the faces we’ve already seen.