 When his father died (1602), Johann Philipp and his younger brothers Frederick, Johann Wilhelm and Friedrich Wilhelm were underage.Because of this, his uncle Johann (more interested in natural sciences and art than politics) took over his guardianship and the regency of his inheritance; but shortly after he took all the duchy of Saxe-Weimar into his own hands.The next year (1603), the young prince of Saxe-Weimar demanded his own inheritance, but his uncle Johann opposed this.