Complex sentence: The Ametrano family were unrelated to the previous holders of the Dukedom of San Donato, but in 1668, the title and the lands were reunited when Amitrano was created 1st Duke of San Donato (of the 2nd creation) by Charles II of Spain.
Split into simpler sentences: The Ametrano family were unrelated to the previous holders of the Dukedom of San Donato, and they held the title in its second creation. However, in 1668, the title and the lands were reunited when Amitrano was created 1st Duke of San Donato (of the 2nd creation) by Charles II of Spain.