Ferdinand III had started out as a contested king of Castile. By the time of his death in 1252, Ferdinand III had delivered to his son and heir, Alfonso X, a massively expanded kingdom. The boundaries of the new Castilian state established by Ferdinand III remained nearly unchanged until the late 15th century. His biographer, Sister María del Carmen Fernández de Castro Cabeza, A.C.J., asserts that, on his deathbed, Ferdinand said to his son "you will be rich in land and in many good vassals, more than any other king in Christendom."