Thirteenth Doctor (The Curse of Fatal Death)

In a universe other than the one that the Renegade Time Lord known as the Doctor called home, the Thirteenth Doctor was the result of the regeneration of the Twelfth Doctor.

Biography
Her previous incarnation regenerated after being hit by zectronic energy.

With the Doctor now regenerated into a woman, she was abandoned by her companion and lover Emma and "his" previous plans to marry her were cancelled. However, the Doctor and the Master found each other much more attractive than before and walked off together as a couple. (TV: The Curse of Fatal Death)