Mary Stuart, Countess of Bute
Mary Stuart, Countess of Bute, 1st Baroness Mount Stuart was the wife of John Stuart, 3rd Earl of Bute, who was Prime Minister of Great Britain between 1762 and 1763.
Lady Bute was born in 1718, the only daughter of Sir Edward Wortley Montagu and Lady Mary Pierrepont, the daughter of the Evelyn Pierrepont, 1st Duke of KingstonuponHull.
Source: Wikipedia