Alternate timeline (The Quantum Archangel)
From Tardis Wiki, the free Doctor Who reference
In one of the many alternate timelines created by the Quantum Archangel, Melanie Bush was the Prime Minister of the United Kingdom and the Third Doctor's exile on Earth was never lifted. She led the fight against a Cybermen invasion. Unfortunately, the Third Doctor betrayed her by siding with the Cybermen. (PROSE: The Quantum Archangel)