"Frederick I, Duke of Saxe-Gotha-Altenburg (15 July 1646 Gotha, Duchy of Saxe-Gotha – 2 August 1691 Friedrichswerth), was a duke of Saxe-Gotha-Altenburg. He was the fourth but eldest surviving son of Ernst I, Duke of Saxe-Coburg-Altenburg and Elisabeth Sophie of Saxe-Altenburg.
When Ernst inherited the duchy of Saxe-Altenburg (1672), he made Frederick the regent of that duchy. In 1674 Ernst, who was already ill, made Frederick the regent of his entire lands.
After the death of his father (1675) Frederick assumed the throne of both duchies. However, on the basis of his family´s house law, he had to allow his six younger brothers to take part in the government. At first, they agreed to a common household of all seven brothers in the Schloss Friedenstein, though this arrangement endured only until 1676." - (en.wikipedia.org 14.06.2020)
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