Andorra is the only country in the world with a political system based on co-princes, that is, with two heads of state. The two co-princes are the President of France and the Bishop of Urgell (a Catholic bishop from Catalonia, Spain). This arrangement dates back to the Pareage of 1278, a medieval treaty that settled disputes between local rulers and gave joint sovereignty to both French and Spanish leaders. Today, both co-princes are largely ceremonial heads of state, while real political power lies with the elected parliament and prime minister.
The two heads of state might be ceremonial, but Andorra does use two postal administrations for it’s mail services (it has no national postal service): the French post office La Poste and the Spanish postal service Correos. Both postal administrations issue their own unique stamps for mail sent from Andorra.
This card appears to be sent via French post.
