“There's such a lot of different Annes in me. I sometimes think that is why I'm such a troublesome person. If I was just the one Anne it would be ever so much more comfortable, but then it wouldn't be half so interesting.” So says 11-year-old Anne Shirley, the preternaturally wise redheaded protagonist of Anne of Green Gables and the nearly one dozen sequels penned in the early 20th century by Lucy Maud Montgomery, a minister's wife from a remote Canadian isle.

From the moment the charming tale of the loquacious orphan girl's rocky upbringing in pioneer Canada hit the shelves in 1908, it was an unexpected instant success. Sequels, and its provincial author, were demanded internationally. If its appeal at its debut a century ago came as a surprise, what's even more shocking is that in the years hence, its popularity has been unflagging. “In 100 years it's never been out of print,” says Kate MacDonald Butler, Montgomery's granddaughter. “Its popularity never seems to be dwindling, there's more and more interest all the time.”

Now, 100 years after its advent, Butler has authorised Before Green Gables, the official account of the one chapter of the ginger-haired girl's life left unexplored by her creator - the beginning. To write her grandmother's prequel, Butler selected one of Canada's foremost children's authors, 81-year-old Budge Wilson, who, like Montgomery, is native to Atlantic Canada. “You need to have a feeling for that part of the world,” Butler says, explaining her choice, “and as an older person, Budge was more connected to the era, more in touch with the time.” This week BGG debuts in the UK; Last month, its first Canadian printing topped the bestseller lists and sold out within a week of publication.

The success is no surprise to Butler, who is the director of the Anne of Green Gables Licensing Authority. A trio of full-time staff handle a “never- ending” barrage of requests for the Anne trademark for a host of products from spoons to dolls to a dozen theatrical adaptations worldwide - there's even an anime cartoon in Japan. The book has sold more than 50 million copies in 36 languages. Prince Edward Island (PEI), the pristine pastoral home of Montgomery and her fictional girl, now revolves around Anne tourism, with 169,000 visitors flooding in last year alone. Some 25 years ago, the island's university established the L.M. Montgomery Institute for “Montgomery Studies”; it includes among its patrons HIH Princess Takamado of Japan. In 1994 she was inducted at Green Gables, visiting the woods and dales that served as the playgrounds of the little heroine's vibrant mind.

It is Anne's astounding imagination, her ability to create so many “different Annes” that sets her apart from the comparatively pedestrian peers of the Laura Ingalls Wilder and Louisa May Alcott variety. Anne has suffered terribly in the years before we meet her - the day of her semi-accidental adoption by a childless couple, the Cuthberts. Yet she retains an indefatigable optimism, fuelled by her incredible ability to imagine. Modern psychology would describe this exercise as her method of escapism; By sheer force of will, she has vanquished her demons.

Anne's always-look-on-the-bright-side mentality forbids her to wallow in self-pity, so the reader only learns of the tribulations the little girl has suffered indirectly. Anne's painful past crops up only in fleeting references, which she avoids when pressed: “‘Oh what I know about myself isn't really worth telling,' said Anne eagerly. ‘...what I imagine about myself you'll think it ever so much more interesting.'” She was beaten and worked from nearly infancy, but dark murmurs are almost immediately glossed over by one of Anne's sweeping flights of fancy, or swiftly mitigated by Montgomery's interludes of rapturous description of the natural beauty of her beloved island.

Thus Budge Wilson, in researching and mapping the saga of Anne's childhood, had to construct a history in the manner of an archaeologist - from just shards. “The puzzle was how she got that way, having lived the difficult way that she lived,” she says. In Before Green Gables we get a clue, finally meeting her glowing, intellectually curious and doomed parents, Walter and Bertha. “I don't feel that genes are a primary factor,” she adds, “but I wanted them in there.” Throughout BGG Wilson puts flesh on the skeletal memories voiced by Anne in the original text. For example, we learn the origin of Anne's only childhood friend - her reflection in the glass of a cabinet door dubbed “Katie Maurice” - and are taken all the way up to the confusion at the orphanage that led to Anne's accidental selection as the Cuthberts' adoptee.

Though Wilson's protagonist is Montgomery's, in accepting the commission she was adamant that the voice be her own. The tone is therefore different: The book is action-driven, filled with wrenching dramatic scenes, whereas Anne of Green Gables revolves around the quaint minutiae of a community as highly mannered as Austen's Bennets and Bingleys. While gripping, in BGG Anne suffers from a lack of her signature bewitching turns of phrase. Most interestingly, characters express what are on face anachronistic sentiments, such as Bertha longing for gender equality. Wilson strongly disagrees. “No matter what time you live in,” she says, “thinking does not change.”

But what is most distinctly different from sunny Anne of Green Gables is that Before Green Gables - in laying bare the saga of injustices wreaked on a special little girl - is a very sad book. According to Butler, Montgomery “set it up to be exactly that, she left all kinds of clues”.

The conspicuous circumambulation of Anne's horrible past combined with the absence of a prequel seem a glaring omission on Montgomery's part - she left no other stone of her character's life unturned. So why didn't she pen a prequel herself?

“She didn't want to talk about miserable stuff,” says Wilson, who studied Montgomery's journals which reveal a personal life fraught with unhappiness. “She got herself above the difficulties of her life by writing.” Like Anne, Montgomery's mother died when she was only nine months old. Her husband was institutionalised for clinical depression, from which she also suffered. “She wrote about sunshine and happy things,” says her granddaughter. “She saved the despair for her journals.”

Before Green Gables is the story Montgomery could never bring herself to divulge. Like Anne, she instead took refuge in her happy imaginings.

Before Green Gables, by Budge Wilson
Puffin, £9.99

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