In a universe other than the one that the renegade Time Lord known as the Doctor called home, a person who logically would have been called the Twelfth Doctor was the result of the regeneration of the Eleventh Doctor.
The twelfth incarnation noted that he had wasted three incarnations in a very short time span simply because he "forgot to unplug". He proved the shortest-lived incarnation, only living long enough to shut off a zectronic energy generator before being hit by excess zectronic energy. He immediately died from the exposure. Allegedly, zectronic energy would kill Time Lords beyond any hope of regeneration. He gave a final speech to Emma and the Master, asking them to "look after the universe" for him, as he had "put a lot of work into it". He promised to explain later, then died. His foes, the Daleks and the Master, vowed to reform and live better lives because of him.
Unexpectedly, he regenerated into a new, female incarnation. (TV: The Curse of Fatal Death)