Oil on canvas, 127cm by 100.3cm. Inscribed l.l. with the identity of the sitter and dated 1775.
Lady Whichcote was an ancestor of Isabella Whichcote of Aswarby Park, Lincolnshire, the only child of Sir Thomas Whichcote, 7th Bt.
In 1875 she married Brownlow, Lord Burghley, who would become the 4th Marquess of Exeter on the death of his father in 1895.
Gainsborough was a founder member of the Royal Academy in 1768 and one of the greatest and most successful portrait painters of the 18th Century.