Portrait of Grand Duchess Maria Fiodorovna by Alexander Roslin, 1777.
Also known as Sophia Dorothea of Württemberg.
Wife of Paul I, mother of Anna Pavlovna (wife of Willem II of the Netherlands, mother of Willem III)
This hangs in The Portrait Gallery of the Romanov Dynasty.

The ugly patches at the side are caused by the windows on this hallway, I already tried to fix them as good as I could. :(