Ciro Santilli's full birth name is "Ciro Duran Santilli", with mother's last name "Duran" in the middle as per Brazilian tradition.
But Ciro's usage of "Duran" got gradually dropped to "Ciro Santilli", Ciro's official Italian name, as Ciro moved more and more definitively to Europe.
It can still however be seen in certain online places where Ciro didn't have the patience or power to change it e.g. some old École Polytechnique stuff:
Also, don't have multiple names if you can avoid it, it is confusing!