Simplify the following text for a Grade 9 native English-speaking person.
Original: Ferdinando was heir to the Grand Duchy of Tuscany , with the title Grand Prince , from his father 's accession in 1670 until his death in 1713 .
Simplified: Ferdinando was heir to the Grand Duchy of Tuscany , with the title Grand Prince from his father 's accession in 1670 until his death in 1713 .