Dad & Germany

so my dad managed to track down his real parents in Germany... through friends who are near Offenbach. Apparently both his parents weren't german after all.. his mother was italian (my grandmother), and his father was german (my grandfather). He had other siblings, and he was the youngest and given away since they couldn't afford to raise more kids. I have to check dad's letters, but their last name was GERMAN. Dad went and visited the only sibling that is still alive, a sister, and she is in the states.. he said there is a massive italian side of the family.