Lady Augusta Murray
Lady Augusta Murray was the first wife of Prince Augustus Frederick, Duke of Sussex, the sixth son of George III. As their marriage was in contravention of the Royal Marriages Act 1772, it was considered legally void, and she could not be styled as the Duchess of Sussex.
Lady Augusta was born in London. Her father was John Murray, 4th Earl of Dunmore and her mother was Lady Charlotte Stewart, daughter of Alexander Stewart, 6th Earl of Galloway. She was styled Lady Augusta Murray at birth, the courtesy title of a daughter of an Earl.
Source: Wikipedia