In 1633 , the Wettin line died out , and Johann Ernst inherited it , but he died heirless in 1638 , and the territories of Saxe-Gotha and Saxe-Eisenach were split between Saxe-Weimar and Saxe-Altenburg . When in 1633 Duke John Casimir died without issue , the Wettin line in Saxe-Coburg died out , and John Ernest inherited it . Nevertheless he himself also died heirless in 1638 , and his territories of were split between Saxe-Weimar and Saxe-Altenburg , which had itself been separated from Saxe-Weimar in 1603 .