Despite her wide circle of friends, and the birth of her daughter Valentine in 1903, Marthe was bored. In 1905, when George was sent by the Romanian king Carol I on a diplomatic mission to Mozzafar-al-Din, Shah of Iran, she eagerly embarked on the trip, recording her observations in a journal. Along the way, she stopped at Yalta, where she encountered the exiled Russian writer Maxim Gorki. It was in 1908, at the suggestion of Maurice Barrès, that Marthe completed and published her impressions of her Persian trip. The French critics and writers were enthusiastic and extremely complimentary. The travel memoirs, "Les Huit Paradis" ("The Eight Paradises"), launched her on a lifelong career as a successful writer of both nonfiction and novels. She became the toast of Belle Epoque Paris, moving easily among the literary, aristocratic and political power elites. She was awarded the Prix de l'Académie française and met Marcel Proust, who sent her a letter praising her book: "You are not only a splendid writer, Princess, but a sculptor of words, a musician, a purveyor of scents, a poet."