CHADDS FORD, Pa. — George Weymouth, a museum founder, conservationist and artist who for years helped hide a secret cache of Andrew Wyeth’s “Helga” portraits, has died.

Weymouth died April 24 at his home in Chadds Ford, according to the Brandywine Conservancy and Museum of Art. He was 79.

Weymouth opened the Brandywine River Museum of Art in 1971 in a converted gristmill as a place to display the works of his lifelong friend Andrew Wyeth.

Nicknamed “Frolic,” Weymouth met Wyeth as a teenager, and the elder artist became Weymouth’s lifelong friend and mentor, teaching him how to paint with tempura.

For years, Weymouth hid a stash of Wyeth’s secret portraits of his neighbor Helga Testorf.

The works, many of them nudes, stunned the art world in 1986 when Wyeth revealed the existence of 240 paintings, watercolors and pencil studies he had done of Testorf from 1971 to 1985. The news was a surprise even to Wyeth’s wife, Betsy.

The highly sensual portraits brought Wyeth millions of dollars and a wave of public attention. They also provided a new window on Wyeth, who some critics viewed as a facile realist, not an artist but merely an illustrator.

Weymouth was also an established painter, known for landscapes, flower studies and portraits, including those of Luciano Pavarotti and England’s Prince Phillip, who was a friend. His paintings are in a number of museums, including the Metropolitan Museum of Art.

Concerned about industrial development in the Brandywine River Valley, Weymouth began buying land along the river in 1967. The conservancy he established has protected about 62,000 acres in Pennsylvania and Delaware.

He was an expert driver of horse-drawn carriages and would hold an annual carriage drive from his 18th century stone manor in Chadds Ford to Winterthur, the former du Pont family estate.

Weymouth’s mother, Dulcinea, was a member of the du Pont family.

Weymouth is survived by his companion, Carlton Cropper; a son, McCoy du Pont Weymouth; a brother, Eugene Weymouth; a sister, Patricia Weymouth Hobbs; ex-wife Anna Brelsford McCoy; and two grandchildren.