Who married Cecilia Underwood, 1st Duchess of Inverness?

Cecilia Underwood, Duchess of Inverness (née Gore and formerly Buggin; c. 1789 – 1 August 1873) was the second wife of Prince Augustus Frederick, Duke of Sussex (sixth son of King George III). Despite marrying, like the Prince's first marriage, their union was in contravention of the Royal Marriages Act 1772 and as such was considered legally void. Consequently, she could not be styled either as the Duchess of Sussex nor a Princess. She was created Duchess of Inverness, in her own right, by Queen Victoria, on 10 April 1840.

Prince Augustus Frederick, Duke of Sussex (27 January 1773 – 21 April 1843), was the sixth son and ninth child of King George III and his queen consort, Charlotte of Mecklenburg-Strelitz. He was the only surviving son of George III who did not pursue an army or navy career. A Whig, he was known for his liberal views, which included reform of Parliament, abolition of the slave trade, Catholic Emancipation, and the removal of existing civil restrictions on Jews and Dissenters.