Complex sentence: Eliza Courtney (1791/92-2 May 1859), ws the illegitimate daughter of Georgiana, Duchess of Devonshire's daughter by Charles, 2nd Earl Grey.
Split into simpler sentences: Eliza Courtney (1791 or 92-2 May 1859), love-child. Eliza was Georgiana, Duchess of Devonshire's daughter by Charles, 2nd Earl Grey.