LONDON (AP) _ Sir Hugh Casson, the former president of the Royal Academy and the artistic mentor of Prince Charles, has died at age 89.

Casson died Sunday after a long illness, the Royal Academy said Monday.

Always modest about his own abilities, Casson headed Britain's oldest and most prestigious art society from 1976 to 1984. But he first started molding Britain's artistic taste decades earlier upon his 1948 appointment as director of architecture for the Festival of Britain.

In a 1984 interview with The Sunday Telegraph, Casson characteristically downplayed his own talents.

He described himself as a generalist, ``a sort of water beetle who skims very fast over the surface but doesn't go very deep.''

Born on May 23, 1910, Casson was educated at St. John's College, Cambridge. After graduating, Casson went to Greece as a Craven Scholar at the British School in Athens.

He returned to England in 1937 and set up a private architectural practice with the late Christopher Nicholson. World War II intervened, and Casson served as a camouflage officer in the Air Ministry from 1940 to 1944.

After the war, Casson continued to work as a private architect while also holding teaching positions at the Royal College of Art.

He was elected to the Royal Academy in 1970, and named its president in 1976.

During his time as president, Casson expanded the number of exhibitions and oversaw some major shows, including ``The Great Japan Exhibition'' in 1982 and ``The Genius of Venice'' in 1983.

But despite his efforts to bring art to the forefront of British life, Casson once declared that the British believe ``beauty is unmanly and should be left to foreigners and women'' and ``art is a very wet exercise done by wet people on wet afternoons.''

During his own architectural career, Casson worked on the interior of the Britannia, the royal yacht, and the Elephant House at the London Zoo.

Casson also persisted with his own watercolor painting, regularly sending his submissions to the Royal Academy for the annual summer exhibition, even after his retirement. He also encouraged Prince Charles in his painting, leading many to label him the prince's artistic mentor.

Sir Philip Dowson, the current president of the Royal Academy, praised Casson on Monday, declaring that ``the Royal Academy, and the visual arts generally, will remain greatly in his debt.''

Casson, who was knighted in 1952, is survived by his wife Margaret and three daughters. Funeral arrangements were not immediately announced.