The House of Dietrichstein was one of the oldest and most prominent Austrian noble families originating from the Duchy of Carinthia. The family belonged to the high nobility (German: Hochadel). The Nikolsburg branch was elevated to the rank of Prince of the Holy Roman Empire in 1624, while a member of the Hollenburg branch was elevated to the same dignity in 1684. The family held two territories with imperial immediacy – the Principality of Dietrichstein, along with castles in Carinthia and Moravia, and the Barony of Tarasp in Switzerland.
Dietrichstein Castle near Feldkirchen in the Duchy of Carinthia was first mentioned in a deed of 1103. It was probably named long before, after a knight Dietrich von Zeltschach, who, in the 9th century, was in the service of the Carinthian dukes. In 1166, the Dietrichstein estates were acquired by the Prince-Bishops of Bamberg and enfeoffed to a family of ministeriales officials, who began to call themselves after the castle. When the line became extinct in the early 14th century, the fief was inherited by Nikolaus I, another Carinthian ministerialis from nearby Nussberg Castle, whose descendants also called themselves von Dietrichstein.
In the late 15th century, the strategically important fortress overlooking the trade route along the Glan valley down to Sankt Veit was occupied by the Hungarian forces of King Matthias Corvinus and finally destroyed by Ottoman invaders in 1483. A new castle was erected below the ruins about 1500 and rebuilt in a Neoclassical style in 1840.In 1514, Siegmund von Dietrichstein (1484–1533) purchased Hollenburg Castle from his father-in-law, the Habsburg emperor Maximilian I, who also elevated him to the noble rank of a Freiherr. He was married to Barbara von Rottal (1500–1550), illegitimate daughter of Emperor Maximilian with Margareta von Edelsheim (d. 1522). In 1572, their son Baron Adam von Dietrichstein (1527–1590) was vested with the extended estates of Nikolsburg (Mikulov) in Moravia by Emperor Maximilian II. Adam's grandson Baron Maximilian II von Dietrichstein was created Graf (Count) on 18 September 1612 and his uncle, the Olomouc bishop Franz von Dietrichstein (1570–1636), was elevated as Fürst (Prince) von Dietrichstein zu Nikolsburg in 1624.
The Nikolsburg branch also acquired the titles of Princely Barony of Tarasp (immediate state of the Holy Roman Empire) in 1684, Count of Proskau in 1769, and Count Leslie of Balquhain in 1802. In 1803 Napoleon annexed Tarasp to his then puppet Switzerland and relocated their lands in Sankt Gallen’s Neuravensburg. After the dissolution of the Holy Roman Empire in 1806 their territory was mediatized by the Kingdom of Württemberg. The line became extinct upon the death of Prince Moritz of Dietrichstein in 1864. Four years later, Alexander von Mensdorff-Pouilly, former Austrian foreign minister and husband of Moritz' cousin Alexandrine, was vested with the title of Prince by Emperor Franz Joseph I. The Princes of Mensdorff-Pouilly-Dietrichstein died out in male line in 1964 in Argentina, as the last Prince only had one daughter, Olga Maria de las Mercedes Theresia Margarete von Dietrichstein zu Nikolsburg (b. 1932).[1]
In 1857, Alexandrine, daughter of Prince Joseph Franz, married Count Alexander von Mensdorff-Pouilly. He served as Foreign Minister and Minister-President of Austria in the 1860s, and in 1868 was created Fürst von Dietrichstein zu Nikolsburg, reviving the title held by his wife's family.
The diplomat Count Albert von Mensdorff-Pouilly-Dietrichstein was a younger son of Prince Alexander Constantin.