Duchy of Saxe-Gotha-Altenburg
|Saxe-Gotha-Altenburg, shown within the other Ernestine duchies, 1826|
|Status||Template:Infobox country/status text|
|Historical era||Middle Ages|
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It was formed in 1672 when Frederick Wilhelm III, the last duke of Saxe-Altenburg died and Ernest I, Duke of Saxe-Gotha (who had married Frederick Wilhelm's cousin, Elisabeth Sophie) inherited his possessions.
The duchy was split up again after Ernest’s death in 1675, and the Duchy of Saxe-Gotha-Altenburg officially came into existence in 1680 when his eldest son, Frederick, took control of the parts of the country Gotha and Altenburg.
When the royal house of Saxe-Gotha and Altenburg became extinct in 1825, Saxe-Gotha was given to Saxe-Coburg-Saalfeld and Saxe-Altenburg passed to the Duke of Saxe-Hildburghausen. After the abolition of German monarchies at the end of the First World War, both Saxe-Gotha and Saxe-Altenburg became part of the newly created state of Thuringia in 1920.
Dukes of Saxe-Gotha-Altenburg
- Ernest I the Pious (1640-1675), inherited Saxe-Altenburg in 1675
- Frederick I (1675-1691), son of Ernest the Pious and the first to be called Duke of Saxe-Gotha-Altenburg.
- Frederick II (1691-1732), son
- Frederick III (1732-1772), son
- Ernest II (1772-1804), son
- Emil (1804-1822), son
- Frederick IV (1822-1825), brother