Based on Hungarian, Lithuanian, Polish, Russian, and Ukrainian sources, this article attempts to determine the identity of Demetrius, “prince of the Tatars,” mentioned in a trade privilege granted to the city of Braşov by Louis I, King of Hungary, in 1368. After examining the sources and the available literature on this subject, the author concludes that Demetrius was perhaps one of the Russian princes ruling at that time: Dmitry Ivanovich, prince of Moscow, or Dmitry Konstantinovich, prince of Suzdal’. The expression “prince of the Tatars” would therefore mean that Demetrius was a vassal of the Golden Horde and not a Tatar from an ethnic point of view, as some scholars believe. Beyond this issue, the article investigates trade relations between Braşov and the East Slavic lands, a topic hitherto neglected by historians who study this Transylvanian city in the Angevin period. The privilege granted to Braşov, conserved in the National Archives of Romania, is presented in the appendix.