Some years before this time he had entered the diplomatic service, being attache, first, at Vienna, then at Rome, then charge d'affaires at Florence. Here he met and married Mathilde Bonaparte, who, through her mother, was closely connected with his sovereign. Nicolai's daughter had been allowed to make a love-match in marrying the duke of Leuchtenberg, son of Eugene Beauharnais, and the emperor was by no means pleased to have another mesalliance in the family. What most offended him, however, was the fact that M. Demidoff, in the Catholic as well as in the Greek marriage ceremony, had promised to educate his children in the faith of the officiating priest. In consequence of this he was deprived of such titular honors as he possessed and was ordered to live abroad. As the married pair did not get on very well, and as, after a childless union of four years, they agreed to separate, Demidoff was again received into the imperial favor. He had meantime bought the fine estate and mansion of San Donato, near Florence; and as he thought the possessor of so much wealth and the husband of so noble a lady deserved to have a title, he dubbed himself "prince," and continued to enjoy this self-given title, probably in the hope that an uncontested use would give him a prescriptive right to bear it. In this hope he was disappointed, for Count Medem, an attache of the Russian embassy at Paris, noticing "Prince Demidoff" on the list of the members of the Jockey Club, crossed the name out, adding the observation, "Il n'y a pas de prince Demidoff." A bloodless duel followed. In the lately-published memoirs of the German novelist Hacklaender--who in 1843 figured as secretary to the crown-prince of Wuertemberg during his visit to Italy--we have an agreeable picture of M. Demidoff at San Donato. "His paintings, sculptures, odd furniture, bronzes and weapons were arranged in an irregular and apparently arbitrary fashion, so that they did not produce the wearisome effect of an ordinary collection, but looked rather like treasures with which their owner had surrounded himself partly for use, partly only to look at." Demidoff "was a tall, thin man," continues Mr. Hacklaender, "with light, almost yellow, complexion, and always dressed with extreme elegance. On the occasion of our first visit to his town-house the princess was painting in her studio, in which art she was more than a dilettante. The prince went first to her with Demidoff, and after they had come back we heard from her a peal of the heartiest laughter, which rung down through five large rooms. Soon after she came out and greeted us in the kindest fashion. She was then a young and handsome woman, with a splendid figure, graceful curves, fine eyes and complexion,--all beautified and illumined by her pleasant voice and happy manner."