Complex sentence: He was best known internationally as the romantic partner of Diana, Princess of Wales, with whom he died in a car crash in the Pont de l'Alma tunnel in Paris along with driver Henri Paul on 31 August 1997.
Split into simpler sentences: He was best known internationally as the romantic partner of Diana, Princess of Wales. He, the princess and their driver Henri Paul died in a car crash in the Pont de l'Alma tunnel in Paris on 31 August 1997.