Complex sentence: On the death of his elder brother Ferdinand in 1578, Diego became heir to the throne, and was formally invested as Prince of Asturias on 1 March 1580 by the Courts in Madrid.
Split into simpler sentences: On the death of his elder brother Ferdinand in 1578, Diego became heir to the throne. He was formally invested as Prince of Asturias on 1 March 1580 by the Courts in Madrid.