The Duke of Clarence

HRH Prince William, Duke of Clarence is a historical figure who was the third child and son of King George III and Queen Charlotte of Charlotte of Mecklenburg-Strelitz. He later became William IV, King of the United Kingdom.

More about him can be discovered on his Wikipedia page.

Arabella
Arabella meets the Duke of Clarence while attending the Chapel Royal, St James, one Sunday with her godmother Lady Bridlington. He talked loudly in church and later greeted Arabella and Lady Bridlington, telling the former that she wore a fetching hat. He is not handsome with a queerly-shaped head and an inclination towards corpulence, but Lady Bridlington says that he is not nearly as fat as the Prince Regent or the Duke of York. His way of speaking reminds Arabella of her uncle Sir John Tallant.