He was physician to the Prince of Wales in 1810. He was also auditor of the Duchy of Lancaster, and from 1821 to 1830 was unofficially private secretary to the king and formally Keeper of the Privy Purse. In an almost unprecedented move, the king surrendered control of his financial affairs to Knighton in 1822, on account of his enormous debts. After three years, in 1825, Knighton declared that the king was free of debt. He had an unparalleled influence over the king, and letters from him to Knighton were addressed "M[y] D[ear] F[riend]," unlike the normal third person that was associated with the sovereign.
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Knighton, Dorothea (1838). Memoirs of Sir William Knighton, Bart. G.C.H. Keeper of the Privy Purse During the Reign of His Majesty King George the Fourth. Including his correspondence with many distinguished persons
Morris, W. I. C. (1976). "Sir William Knighton. The Invisible Accoucheur". Manchester Medical Gazette55(2) 46–50