Okay, I've decided to share this, because it really blew my mind, although an explanation is ridiculously simple...

So, remember how Clara asked Missy in The Magician's Apprentice since when has she [Missy] cared about the Doctor? Quoting the response:

"Since always. Since the Cloister Wars. Since the night he stole the moon and the President’s wife. Since he was a little girl. One of those was a lie – can you guess which one?"

We all assumed that Missy took a twist on the 'Arson, Murder, and Jaywalking' Trope and that the last one was a lie. I mean, we know for a fact that every regeneration of the Doctor was male, right?

Well now, remember Hell Bent and Twelve and Clara in the Cloisters? He said that the claim he "stole the moon and the president's wife" is a lie. Now, if we're believe that Missy really only told ONE lie that time...

Then we have something to think about, don't we?