Vincent Van Gogh's paintings of sunflowers, which hang in the National Gallery in London and the Neue Pinakothek in Munich, are among the most celebrated works of art in the world.
Yet the Dutch artist also painted two lesser-known canvasses in the same week with the same subject, dubbed the Hidden Sunflowers.
Now an expert has traced one, which has not been seen by the public for more than 60 years, and found an image of the other, which was destroyed in a bombing raid during World War II and had rarely been seen outside Japan.
Martin Bailey, a Van Gogh specialist, tracked down the unknown Sunflowers during research for his book The Sunflowers are Mine: The Story of Van Gogh's Masterpiece.
The book also reveals that the artist turned to the flowers because the life models he was intending to paint failed to turn up, and the weather was so poor that landscape painting was impossible.
Of Three Sunflowers, the painting that survives, and Six Sunflowers, which was destroyed in Japan, Bailey said: "These are the hidden Sunflowers that are never seen.
Both are fully authentic and accepted by Van Gogh scholars."
Van Gogh painted four original Sunflower works in Arles, Provence, in 1888, before creating three copies some months later.
Bailey said: "There is something magical about them and it's hard to put one's finger on it."
Bailey, a correspondent for The Art Newspaper, said the four original paintings were completed in less than a week, twice as fast as previously assumed. The three copies Van Gogh painted later are now on show in museums in Philadelphia, Amsterdam and Tokyo.