Complex sentence: The historical Chauvelin was in fact a notable military officer who served with Rochambeau in the American Revolution, the assistant ambassador to England in the time period depicted, was never a member or an agent of the Committee of Public Safety and survived Thermidor.
Split into simpler sentences: The historical Chauvelin was in fact a notable military officer who served with Rochambeau in the American Revolution, and as assistant ambassador to England in the time period depicted. The real Chauvelin was never a member or an agent of the Committee of Public Safety, and survived Thermidor.