Warne was among the six publishers whom Beatrix Potter submitted her first book, the story of a rabbit called Peter. Like the other five firms, Warne turned the proposal down. But the people at the firm changed their minds when they saw the privately published copy in 1901. They said they would publish the book, as long as the illustrations were drawn in colour. The next year, Warne published "The Tale of Peter Rabbit", and by Christmas it had sold 20,000 copies. This began a 40-year partnership that saw the publication of 22 additional little books. Beatrix Potter was engaged to marry Norman Warne, her editor and the youngest of the three Warne brothers. However, he died tragically in 1905, only a few weeks after their engagement. Harold, the eldest brother, took over as Potter's editor. She continued to produce one or two new Little Books each year for the next eight years until her marriage in 1913 to William Heelis. During the next few years Potter turned her attention to her farm work, but when the company fell on hard times and Harold was imprisoned for embezzlement, she came to the rescue with another new title to support "the old firm." Potter, who had no children, left the rights to her works to Warne upon her death. The company continued to publish them; it also brought out several biographical works about its most renowned author. Over the years, Warne also expanded its nonfiction publishing, issuing among others the world-famous Observer books.