Complex sentence: He was killed by a gunshot at the Battle of Quatre Bras on 16 June, the night after he had attended the Duchess of Richmond's ball in Brussels and left it happy to have a chance to show his fighting ability.
Split into simpler sentences: He was killed by a gunshot at the Battle of Quatre Bras on 16 June. The night after he had attended the Duchess of Richmond's ball in Brussels and left it happy to have a chance to show his fighting ability.