Parallel universe (Exile)
From Tardis Wiki, the free Doctor Who reference
In one parallel universe, a version of the Doctor was pursued by the Time Lords. He commited suicide by jumping off a pylon in an attempt to avoid capture, and in the process regenerated into a female. The Doctor then began to hide on Earth.
In this universe it was against the law of the Time Lords to regenerate into a different gender. (AUDIO: Exile)
This dimensions War Lord and his people were dematerialised by the Time Lords.
Other alien races that were mentioned to have appeared included the Quarks.
If you'd like to talk about narrative problems with this story — like plot holes and things that seem to contradict other stories — please go to this episode's discontinuity discussion.