The marriage was initially childless, so in 1605 he legitimised Ottavio and recognised him as his successor and heir to the dukedom.
From 1607 to 1620 Ottavio was feudal lord of large estates, both in the Duchy of Parma – including Borgo San Donnino, Fiorenzuola and the Val di Nure – and lands inherited from his great-grandmother Margaret of Austria in the Kingdom of Naples, including Altamura, Campli, Castellamare, Cittaducale, Leonessa, Montereale, Ortona, Penne and Roccaguglielma.
[1] The suggestion that he married Sofronia Sanvitale, daughter of Girolamo, marchese of Sala Baganza and Colorno, is spurious; she never existed.
[1] In 1610 Ranuccio's wife had a son, Alessandro, but he proved to be deaf and was felt incapable of succeeding him.
Ottavio organised a conspiracy against his father, but this failed and he was stripped of his titles and imprisoned in Parma in 1621.