Thirteenth Doctor (The Curse of Fatal Death)

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".