Ernst II Bernhard Georg Johann Karl Frederick Peter Albert, Duke of Saxe-Altenburg (b. Altenburg, 31 August 1871 – d. Trockenborn-Wolfersdorf, 22 March 1955), was the last reigning duke of Saxe-Altenburg.
He was the fourth child but only son of Prince Moritz, the youngest son of Georg, Duke of Saxe-Altenburg and Princess Augusta of Saxe-Meiningen.
The death of his father on the 13 May 1907 made him first in the line of succession to the duchy of Saxe-Altenburg. He inherited the dukedom when his uncle and namesake Ernst I, died without surviving male issue, on the 7 February 1908.
On 27 February 1898 in Bückeburg Ernst married his first wife, Princess Adelaide of Schaumburg-Lippe, a granddaughter of George William, Prince of Schaumburg-Lippe. They had four children:
- Princess Charlotte Agnes (Potsdam, 4 March 1899 – Hemmelmark bei Eckernförde, 16 February 1989); married on 11 July 1919 Prince Sigismund of Prussia.
- Georg Moritz, Hereditary Prince of Saxe-Altenburg (Potsdam, 13 May 1900 – Rendsburg, 13 February 1991).
- Princess Elisabeth Karola (Potsdam, 6 April 1903 – Breiholz, 30 January 1991).
- Prince Frederick Ernst (Potsdam, 15 May 1905 – Rosenheim, 23 February 1985).
During World War I, Ernst refused all honorary appointments at the Kaiser's headquarters (which would have been considerably safer than other areas). He renounced his rank as General, entered the service as a Colonel, and distinguished himself at the Battle of Péronne. By the end of the war, he was a commander of a division.
A great lover of science, Ernst had a wireless installation fitted inside his castle in Altenburg during the start of the war. Its purpose was to specially communicate with airships. Ernst also had a lifelong interest in wireless telegraphy and telephony, and was considered an expert of aeronautics.
When Germany lost the war, all the German princes lost their titles and states. Ernst was one of the first princes to realize major changes were coming for Germany, and quickly arrived at an amicable settlement with his subjects. He was forced to abdicate the government of the duchy on 13 November 1918, and spent the rest of his life like a private citizen.
After his abdication Ernst, with a moderate fortune, retired to a hotel in Berlin. Two years later, in 1920, his marriage ended in divorce. Later the same year, Ernst announced his engagement to Helena Thomas, an opera singer. They had met while she was temporarily filling an engagement at the Ducal Theatre in Altenburg during the war. The marriage never took place however.
On 15 July 1934 Ernst married his second wife Maria Triebel, who had been his companion for many years, at his home, Schloss Froehliche Wiederkunft ("Palace of Happy Returnings"). Maria was born in Waltershausen on October 16, 1893, and died in Trockenborn-Wolfersdorf on February 28, 1955. This was a morganatic marriage, and she received only the title of "Baroness Reiseneck". They had no children.
Still interested in science Ernst established a modern observatory in Wolfersdorf, employing Kurd Kisshauer in 1922. On 1 May 1937 Ernst joined the Nazi Party
Ernst became the only former reigning German prince who accepted German Democratic Republic citizenship after World War II, refusing an offer to leave his beloved Schloß Fröhliche Wiederkunft and relocate to the British occupation zone. The Schloß had been confiscated by the Soviet occupiers, but Ernst had been granted free use of it until his death. In March 1954, with the death of Charles Edward, Duke of Saxe-Coburg and Gotha, he became the last survivor of the German princes who had reigned until 1918. One year later, on 22 March 1955, he died at his Schloß.