Rosamund Clifford (c. 1150 - c. 1176) was Henry II of England's mistress. Unluckily for her, his wife was Eleanor of Aquitaine, who was not at all fond of The Fair Rosamund.
Mary, Queen of Scots, is famous for being executed by her cousin, Queen Elizabeth I. Before her beheading, Mary wrote a letter to her brother-in-law, Henri III.
Sibylle of Cleves was a sister-in-law of Henry VIII who is all but forgotten. She was the eldest daughter, a mother of four Johns, and a brave defender of Wittenberg.
One tends to remember an Empress of Austria more than a Princess of Thurn and Taxis. But Helene in Bavaria led a much happier life away from the imperial throne.
Very few women in history have betrayed their sisters to become the king's mistress. Maybe that's why Marie Anne de Mailly, arguably history's worst sister, is so intriguing.
Marie Antoinette of Austria was the Queen of France who had the bad luck of being consort during the French Revolution. Here is her last letter.
Marozia of Tusculum was the closest thing we had to a female pope. Pope Joan was probably a myth, but we can be sure Marozia existed, since she was related to seven popes.
Tarabai was a very important figure in history. Without her, there may never have been any Rajas of Kolhapur, and perhaps no long-lasting Maratha Empire either.
Empress Sisi had a very long and very miserable life at the Austrian court, becoming Empress at just fifteen, even though she never wanted the role.
Berengaria of Navarre became Queen of England in the 1100s, but because her husband was always on crusade, she never got to settle down in England.