Earl of Munster in the context of "Courtesy title"

Duke of Clarence and St Andrews was a title created in 1789 in the Peerage of Great Britain for Prince William Henry (later King William IV). He was also created Earl of Munster in the Peerage of Ireland at the same time.

While there had been several creations of Dukes of Clarence (and there was later a Duke of Clarence and Avondale), the only creation of a Duke of Clarence and St Andrews was for Prince William, third son of King George III. When William succeeded his elder brother George IV to the throne in 1830, the dukedom merged in the crown. The title refers to ancient castle and honour of Clare, Suffolk; and the Scottish city of St Andrews.

The FitzClarence family was an illegitimate branch of the House of Hanover. Prince William, Duke of Clarence and St Andrews, who later became King William IV of the United Kingdom, had at least ten children with his mistress Dorothea Jordan, all of whom took the surname FitzClarence. All of them were also granted by their father the rank of a marquess' younger sons or daughters.

The Duke of Clarence's eldest surviving illegitimate child, George FitzClarence (1794–1842), was created Earl of Munster in 1831 and his male-line was continued until the death of the 7th Earl of Munster in 2000. Two of Lord Munster's brothers, Frederick and Augustus (a clergyman), had issue that were also part of the family. Five daughters of William IV and Dorothy Jordan were married to nobles or prominent military figures, including the 18th Earl of Erroll, the 10th Viscount Falkland, and Admiral Lord John Hallyburton. Only one, Mary, had no children.