Beatrix Potter's "The Tale of Kitty-In-Boots," which was found among her memorabilia two years ago, is set to be published in September by Penguin Random House (PRH). Following the announcement on Tuesday, the book has been steadily climbing Amazon U.K.'s bestselling list since, according to Quartz.

The long-lost book is about a "well-behaved prime black kitty cat, who leads rather a double life," per BBC. It also features an "older" and "slower" character that alludes to Peter Rabbit, which is from the British author's bestselling classic, "The Tale of Peter Rabbit."

PRH publisher Jo Hanks stumbled upon the book while reading an out-of-print biography on Potter, which referenced a letter the author sent to her publisher in 1914, according to ABC News. Hanks then visited the Victoria and Albert Museum in London and found three forgotten manuscripts handwritten in notebooks. Potter also apparently had a rough sketch of Kitty and the Mr. Tod, the elderly arch-villain.

An unknown #BeatrixPotter story called #TheTaleOfKittyInBoots is to be published for the first time in September 2016, 100 years after it was written, with illustrations by #QuentinBlake. It was found in the archives at #TheVictoriaAndAlbertMuseum in #London and will include Potter's much loved characters including an older, fatter Peter Rabbit. So excited.

A photo posted by karan (@karan1308) on Jan 27, 2016 at 10:12am PST

The main character goes by the name Miss Catherine St. Quentin, but by night, she's the gun-toting "Q" or "Squintums," who wears "a gentleman's Norfolk jacket and little fur-lined boots" while chasing bad guys, according to The Telegraph.

Bookish News, my friends! Newly discovered #BeatrixPotter story to be published in September by her original publishers. "Quentin Blake to illustrate The Tale of Kitty-In-Boots, which was left unfinished when Potter died and was lost for more than a century." The Guardian News The Tale of Kitty-in-Boots was left unfinished & lost for over 100 years! This is an exciting day to be a British literature junkie. #joyfulandbookish #booknerdissues A photo posted by Heather Mac (@livingbooksnook) on Jan 26, 2016 at 6:59am PST

Hanks further revealed that Potter planned to finish the book, but she was interrupted by "World War I, marriage and illnesses." With only one sketch done, PRH commissioned Roald Dahl illustrator Quentin Blake to create more drawings for "The Tale of Kitty-In-Boots."

"The tale really is the best of Beatrix Potter. It has double identities, colorful villains and a number of favorite characters from other tales - most excitingly, Peter Rabbit makes an appearance, albeit older, slower and portlier," said Hanks via The Bookseller.

PRH plans to publish the book in time for Potter's 150th birthday.