Sir John Charles Buchanan Riddell, 13th Baronet, KCVO KStJ DL FRSA (3 January 1934 – 24 July 2010) was Private Secretary to the Prince of Wales from 1985 to 1990. He was Lord Lieutenant of Northumberland from 2000 to 2009. Riddell was born at Hepple, Northumberland. He succeeded to the Baronetcy of Riddell of Riddell as an infant, on the death of his father in 1934. The family seat at Whitefield House, Hepple was bought by his ancestor Sir John Buchanan Riddell (1796–1822) from the Duke of Portland in 1804.