Complex sentence: When Westphal died on 12 January 1875, he was the last surviving Royal Navy officer to have fought at Trafalgar on board HMS "Victory" and had lived until the age of 90, some 70 years after seeing Nelson die.
Split into simpler sentences: When Westphal died on 12 January 1875, he was the last surviving Royal Navy officer to have fought at Trafalgar on board HMS "Victory". He had lived until the age of 90, some 70 years after seeing Nelson die.