Saxe-Gotha-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.