Historical Royal Blind Item #2: You Are Not the Father!

A German born princess has caught the eye of an Imperial Russian prince. She is beautiful, educated and most importantly, of high birth. Or is she? The prince's father is not happy about what he has heard. Allegedly the German princess' mother was not faithful to her ducal husband. After being neglected for many years, the mother shacked up with her husband's stable master! Everyone knows that Princess is not the Duke's daughter. Her resemblance to the handsome stable master is apparent, which supposedly angers the Duke. However, he has accepted this daughter and her younger brother as his own. Is this acceptance enough for the Tsar to allow Princess to marry his son?

Can you name the princess in this royal blind item?