Eva Merthen (1723–15 October 1811), known as "The Duchess of Finland", was a Finnish woman known for her relationship with the General James Keith during the Russian occupation of the Swedish province of Finland during the Russo-Swedish War (1741–1743).
She made the acquaintance of Keith, who was the leader of the Russian forces who captured Åbo in 1742, at the receptions arranged by the Russian officers and where she made a success as a well-educated, charming beauty.
[2] Her father died shortly before the peace in 1743, and when Keith left Finland, she followed him.
They were never technically married, but she was treated by Keith as well as by society as his official and legal spouse, especially after he joined Prussian service.
After the death of Keith in 1758, she married in 1760 to the politician Johann David von Reichenbach (1732–1807) in Stralsund.