 In 1583, John Casimir became regent, and Junius was invited back to become professor of theology at the University of Heidelberg.From the late 1580s to 1592, Junius participated in diplomatic missions for the duke of Bouillon in France and Germany, which involved meeting personally with the king of France, Henry IV of Navarre.In 1592, he was named professor of theology at the University of Leiden.