Complex sentence: Elizabeth Conyngham ("née" Denison), Marchioness Conyngham (31 July 1769--11 October 1861), was an English courtier and noblewoman, and the last mistress of George IV of the United Kingdom.
Split into simpler sentences: Elizabeth Conyngham ("née" Denison), Marchioness Conyngham (31 July 1769--11 October 1861), was an English courtier and noblewoman. She was the last mistress of George IV of the United Kingdom.