Thirteenth Doctor (The Curse of Fatal Death)
From Tardis Wiki, the free Doctor Who reference
The Thirteenth Doctor was the last, female incarnation of the Doctor. With the Doctor now regenerated into a woman, she abandoned her companion Emma and "his" previous plans to marry her. The Doctor and the Master fall in love.
Real World
Fans had for years, thought Joanna Lumley a candidate for the role of the Doctor, should they ever cast a woman in the role. (She had earlier played Sapphire, a non-human time detective in the cult fantasy series Sapphire & Steel.) The script gave her name as "The (Female) Thirteenth Doctor".
