Complex sentence: Harriman was one of the aristocratic set from the US Embassy, charming, suave and sophisticated, they had developed a friendship during the London Blitz, so that by 17 April 1941 they were already close and intimate friends.
Split into simpler sentences: Harriman was one of the aristocratic set from the US Embassy, charming, suave and sophisticated. They had developed a friendship during the London Blitz, so that by 17 April 1941 they were already close and intimate friends.