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"The Tale of Kitty-in-Boots" was found two years ago in a letter Potter sent to her publisher in 1914. It mentioned "a well-behaved prime black Kitty cat, who leads rather a double life," referring to an unedited version of the story, The Guardian reported.

A search through a London archive found three handwritten manuscripts and a rough color sketch of the main character. It also contained a pencil sketch of the villain, Mr. Tod.

Potter planned to finish the story, but was interrupted by World War I, marriage, sheep farming and colds.

Potter died in 1943 and the story went unfinished.

Quentin Blake has lent his colors to the story. Blake illustrated Roald Dahl's books like "Charlie and the Chocolate Factory."

"The Tale of Kitty-in-Boots" will be published in September by Frederick Warne & Co, the original publisher for Potter's books.