Complex sentence: One of the key figures in the negotiations was Pierre Louis Napoleon Cavagnari, a half-Irish, half-Italian aristocrat, descended from the royal family of Parma on his father's side, who had been brought up in England, with schooling at Addiscombe.
Split into simpler sentences: One of the key figures in the negotiations was Pierre Louis Napoleon Cavagnari. A half-Irish, half-Italian aristocrat, descended from the royal family of Parma on his father's side, he had been brought up in England, with schooling at Addiscombe.