Complex sentence: Green was the first non-French national to be elected to the Académie française in 1971, because everybody thought he had dual citizenship, but he never became a french citizen although he was born in Paris and wrote in french.
Split into simpler sentences: Green was the first non-French national to be elected to the Académie française in 1971, because everyone thought he had dual citizenship. In fact, he never became a French citizen although he was born in Paris and wrote in French.