Complex sentence: Frederick Francis of Brunswick-Wolfenbüttel (born 1732, died 14 October 1758 at the Battle of Hochkirch) was Frederick the Great's brother-in-law.
Split into simpler sentences: Frederick Francis of Brunswick-Wolfenbüttel born 1732, died 14 October 1758 at the Battle of Hochkirch. He was Frederick the Great's brother-in-law.