 His father, Cosimo II, died on 28 February 1621; he was succeeded by Ferdinando de' Medici, the elder son.On 29 May 1629, Grand Duke Ferdinando appointed Mattias governor of Siena, following the death of their aunt and the then governor, Catherine de' Medici.He arrived in his domain on 27 August and took up residence in the Piazza del Duomo.