When he became Swedish royalty , he had also been the Sovereign Prince of Pontecorvo in Central-Southern Italy from 1806 until 1810 ( title established on June 5 , 1806 by Napoleon ) , but then stopped using that title .
Before he became Swedish royalty , he had also been the Sovereign Prince of Pontecorvo from 1806 until 1810 , but then stopped using that title .