Pier Luigi was also Duke of Castro, a title he was bestowed upon by his father, after the latter created it from the lands recovered after the death of Ranuccio the Elder, Pier Luigi's younger brother.
Pier Luigi a fost, de asemenea, Duce de Castro, un titlu conferit de către tatăl său, după ce acesta din urmă a creat teritoriul din ținuturile recuperate după moartea lui Ranuccio cel Bătrân, fratele mai mic a lui Pier Luigi.