Who was writing to Grand Duke Adolphe in 1893?

Here’s a cover franked with a 25-centime French Sage definitive [Sc 91]

that was posted to

Son Altesse Royale [His Royal Highness]
le grand duc de Luxembourg
à Luxembourg

from Gare de Cannes, Alpes-Maritimes, France, on March 9, 1893. The back shows the receiving cancels of Luxembourg-Ville and the post office at the Grand Ducal residence—Walferdange (Chateau)—two days later.

In 1893, the Grand Duke of Luxembourg was Adolph of Nassau-Weilburg (July 24, 1817 to November 17, 1905), who was the last Duke of Nassau, and the fourth Grand Duke of Luxembourg. The only indication of the sender’s identity is on the back flap where there is a raised “N” below a crown. Does the “N” refer to the House of Nassau? Was the Grand Duke, himself, or other royalty, enjoying a holiday at Cannes on the French Riviera? Certainly some astute philatelist will provide the answers.

Grand Duke Adolph was a son of Wilhelm, Duke of Nassau (1792-1839). He became Duke of Nassau on August 30, 1839, after the death of his father. He supported the Austrian Empire in the Austro-prussian War of 1886. After Austria's defeat, Nassau was annexed to the Kingdom of Prussia. In 1890, when Queen Wilhelmina of the Netherlands was excluded from succession to the Luxembourg throne by the Salic Law, the Grand Duchy passed to the dispossessed Duke Adolphe. The Grand Dukes of Luxembourg are still descendants of Adolphe, although through female lines. Walferdange Chateau, five kilometers north of Luxembourg-Ville near the entrance of the Grunewald forest (shown at the top), was the grand ducal residence at the turn of the 19th century.

Grand Duke Adolphe