 The ultimate heir of his four grandparents, he inherited all of his family dominions at a young age, due to the premature death of his father and the mental illness of his mother.After the death of Philip in 1506, he inherited the Burgundian Netherlands, originally held by his paternal grandmother Mary.In 1516, he became co-monarch of Spain with his mother Joanna, and as such he was the first king of Spain to inherit the country as dynastically unified by the Catholic Monarchs, his maternal grandparents.