Melusine Ermengarde van der Shulenberg (sp?) I believe was the name. What a glorious mouthful it is. :-)
The other mistress's name was more conventional, yet still gorgeous.
Charlotte Sophia Kellmans (sp?), but I'm not as certain of this one.
One was very thin and the other was very fat. The English court called them "Elephant and Maypole." That might help in a google search.