Prince Regent [Prince Regent] BrE NAmE the title of George, ↑Prince of Wales (later King ↑George IV), who ruled Britain from 1811 to 1820 while his father, King ↑George III, was mentally ill. ↑Regent Street and ↑Regent's Park in London are named after him, and the period 1811–20 is known as the ↑Regency.