Complex sentence: Rowling originally believed he had won the Légion d'honneur during the war, as she said when she received it herself in 2009; she later discovered the truth when featuring in an episode of the UK genealogy series "Who Do You Think You Are?".
Split into simpler sentences: Rowling originally believed he had won the Légion d'honneur during the war, as she said when she received it herself in 2009. She later discovered the truth when featuring in an episode of the UK genealogy series "Who Do You Think You Are?".