Complex sentence: Michael assumes this is due to his Jewish heritage, however it is later revealed that Leo was born Axel Bauer, the son of Dietrich Bauer, a Nazi doctor at Auschwitz.
Split into simpler sentences: Michael assumes this is due to his Jewish heritage. However, it is later revealed that Leo was born Axel Bauer, the son of Dietrich Bauer, a Nazi doctor at Auschwitz.