Wallis Simpson

 was the divorced American mistress and later the wife of the former King Edward VIII of the United Kingdom. She met the Sixth Doctor and Peri Brown in 1936, shortly before Edward abdicated the British throne to marry her on 10 December of that year. (PROSE: Players)

In an alternative timeline in which Nazi Germany won World War II, Edward VIII was restored to the throne with Wallis as his Queen in 1940. He signed a treaty which established Great Britain as a protectorate of the Greater German Reich. (PROSE: Timewyrm: Exodus)

Behind the scenes
The Brilliant Book 2011 claims that Simpson is a shape-shifter.