text: In 1668 he died , just before of the birth of his fifth son , Willam Augustus , who became the new Duke of Saxe-Eisenach from his birth , under the guardianship of his uncle John George .
simplified: In 1668 he died , just before of the birth of his fifth child , Wilhelm August , who became the new Duke of Saxe-Eisenach from his birth , with Johann Georg as regent .