LONDON — Until recently, visitors to the headquarters of one of Prince Charles’s charities in Scotland could say that they had seen, among other artworks, three paintings by Claude Monet, Pablo Picasso and Salvador Dalí.

Or so they thought.

A well-known American art forger says that the paintings — displayed at Dumfries House, an 18th-century estate that stretches across 2,000 acres and houses the headquarters of the Prince’s Foundation, one of Prince Charles’s charities — were not actually the works of modern masters.

He says he painted them himself.

The forger, Tony Tetro, said in an email on Monday that he had painted at least three works that were lent to the charity — pieces that The Times of London reported had an estimated value of 100 million pounds , or about $129 million.

A spokesman for the Prince’s Foundation confirmed on Monday that the authenticity of the paintings, which have been removed from display, was in doubt.