The first duke of Saxe-Coburg and Gotha was Ernest I, who reigned from 1826 until his death in 1844. He had previously been Duke of Saxe-Coburg-Saalfeld from 1806 until the duchy was reorganized in 1826. Ernest's younger brother Léopold became King of the Belgians in 1831, and his descendants continue to serve as Belgian monarchs. Léopold's only daughter, Princess Charlotte of Belgium, was the consort of Maximilian I of Mexico, and she was known as Empress Carlota of Mexico in the 1860s. Ernest I's second son, Prince Albert, married Queen Victoria in 1840, and thus is the progenitor of the United Kingdom's royal family, called the House of Windsor since 1917. In 1826, a cadet branch of the house inherited the Hungarian princely estate of the Koháry and converted to Roman Catholicism. Its members managed to marry a queen regnant of Portugal, an imperial princess of Brazil, an archduchess of Austria, a French royal princess, a royal princess of Belgium and a royal princess of Saxony. A of this branch, Ferdinand, became ruling Prince and then Tsar of Bulgaria, and his descendants continued to reign there until 1946. The current head of the House of Bulgaria, the former Tsar Simeon Saxe-Coburg-Gotha, who was deposed and exiled after World War II, goes by the name of Simeon Sakskoburggotski and served as Bulgaria's prime minister from 2001 to 2005. The ducal house consisted of all male-line descendants of John Ernest IV, Duke of Saxe-Coburg-Saalfeld legitimately born of an equal marriage, males and females, their wives in equal and authorised marriages, and their widows until remarriage. According to the House law of the Duchy of Saxe-Coburg and Gotha, the full title of the Duke was: There were two official residences, in Gotha and Coburg. Therefore, the whole ducal court, including the court theatre, had to move twice a year: from Gotha to Coburg for the summer and from Coburg to Gotha for the winter. For the Court Theater, two almost identical buildings had to be built in 1840 in Gotha and Coburg and thereafter maintained at the same time. In addition to the residential castles, Friedenstein Palace in Gotha and Ehrenburg Palace in Coburg, the ducal family also used the Schloss Reinhardsbrunn in Gotha, as well as the Schloss Rosenau and Callenberg Castle in Coburg, and a hunting lodge, Greinburg Castle, in Grein, Austria.
Although the ducal branch is eponymous with the dynasty, its head is not the senior member of the family genealogically or agnatic. In 1893, the reigning duke Ernest II died childless, whereupon the throne would have devolved, by male primogeniture, upon the descendants of his brother Prince Albert. However, as heirs to the British throne, Albert's descendants consented and the law of the duchy ratified that the ducal throne would not be inherited by the British monarch or heir apparent. Therefore, the German duchy became a secundogeniture, hereditary among the younger princes of the British royal family who belonged to the House of Wettin, and their male-line descendants. Instead of Albert Edward, Prince of Wales inheriting the duchy, it was diverted to his next brother, Prince Alfred, Duke of Edinburgh. Upon the latter's death without surviving sons, it went to the youngest grandson of Prince Albert and Queen Victoria, Prince Charles Edward, Duke of Albany. Charles Edward's uncle Prince Arthur, Duke of Connaught and his male line had renounced their claim. Although senior by birth, they were either not acceptable to the German Emperor as either a member of the British military or unwilling to move to Germany. The current head of the ducal branch is Andreas, the grandson of Charles Edward. Since the duchy was abolished in 1918, the heads use the title Prince rather than Duke.
Because of the First World War, the title of the family was unofficially changed in 1920 or 1921 to "of Belgium", and the armorial bearings of Saxony were removed from the Belgian royal coat of arms. Since the 2017 Carnet Mondain, the title "Saxe-Cobourgh-Gotha" is again in use for all the descendants of Leopold I, with the exception of King Philippe, his wife, his brother and his sister who keep their title "of Belgium"; therefore the descendants of Astrid of Belgium do not bear this title, but that of "of Austria-Este" of their father. The armorial bearing of Saxony was put back in 2019.
, descent as reckoned from father to son, had historically been the principle determining membership in reigning families until late in the 20th century, thus the dynasty to which the monarchs of the House of Saxe-Coburg-Gotha belonged genealogically throughout the 1900s is the House of Wettin, despite the official use of varying names by different branches of the patriline.
