The Thirteen

The Thirteen was the hypothetical thirteenth and final incarnation of a Renegade Time Lord who suffered from regenerative dissonance, following the Twelve. When trying to work out the identity of, Liv believed him to be the Thirteen. (AUDIO: Day of the Master)

After speculating about the possible demise of the Twelve, the Eighth Doctor belived it was inevitable that he will eventually cross paths wth the Thirteen. (AUDIO: Dreadshade)