Sarah and Daniel Chatto + David and Serena attended a gala dinner celebrating the opening of the 'Christian Dior: Designer of Dreams' exhibition at The V&A in London
The man at far right (and in the picture with Lady Frances): Daniel Chatto , husband of Sarah.
The blond woman second from the right: Serena, countess of Snowdon (née Serena Stanhope), wife of David.
And Lady Frances von Hofmannsthal, is a daughter from Anthony Armstrong Jones (1st Lord Snowdon) of his second marriage. Anthony, who deceased in 2017, is the father of David and Serena.
Which 4th person did you mend?