His tummy as portly as it always would be, Winnie-the-Pooh’s very first appearance has been revealed in a previously unpublished sketch from the 1920s by illustrator EH Shepard.

The Art of Winnie-the-Pooh brings together more than 150 images, 80 of which have never been seen or published before, from archives of Shepard’s work. Published next week, the book reveals the genesis of his iconic illustrations of theworld’s most beloved teddy bear, as well as the correspondence and collaboration with AA Milne that went into Pooh’s creation. The documents were found by James Campbell, who is married to Shepard’s great-granddaughter and has run his estate since 2010.

Facebook Twitter Pinterest EH Shepard’s first known drawing of Winnie-the-Pooh, based on Growler. Photograph: © EH Shepard/The Shepard Trust

“EH Shepard kept a vast amount of material throughout his very long working life – he was still working at the age of 95. Towards the end of his life, he sorted out his material, and he basically gave away everything he thought was of value … On his death, he said in notes to his executors that all of the material left was essentially of no value – scribblings and sketches. So as a result, no one looked into it for 30 years,” said Campbell.

When Campbell took over the estate, he was approached by organisations looking for material by Shepard about the first world war. “We started looking through this supposed pile of rubbish, and not only discovered material relating to the war, but … all sorts of preparatory drawings and sketches for Winnie-the-Pooh, early drafts and autobiographical material,” said Campbell. “We discovered a lot of writing he’d done that wasn’t published, but which throws interesting light on the relationship between him and Milne, how they worked collaboratively together.”

Besides the page from a 1920s sketchbook showing what is believed to be the first drawing of Milne’s Bear of Very Little Brain, it includes what Campbell writes “must be one of the very earliest complete iterations of Winnie-the-Pooh, drawn as just a few lines of soft pencil, holding what looks like a barrel, which was surely to become a jar of honey”.

“You can see how sketches with a few lines build up into the final illustrations we know and love,” said Campbell.

The book also shows how the look of Pooh developed: as is widely known, he was inspired by Milne’s son Christopher Robin’s toy bear, but Campbell said that the soft toy was decided by the artist and the writer to not have quite the right appearance. “Both he and AA Milne realised that Christopher Robin’s bear was too gruff-looking, not very cuddly, so they decided they would have to have a different bear for the illustrations. When Shepard got home, he remembered his son Graham had a teddy bear, so he drew this bear and sent it to Milne, who said it was perfect. So [the illustration] is actually based on a bear called Growler,” said Campbell.

Facebook Twitter Pinterest ‘Too gruff-looking’ … EH Shepard’s initial sketch for Winnie-the-Pooh, based on AA Milne’s son’s toy. Photograph: © EH Shepard/The Shepard Trust

The illustrations of Christopher Robin are also shown to spring from Shepard’s own life as well as Milne’s. “The drawings … are partly from life, but are also inspired by aspects of Shepard’s son Graham. Christopher Robin is a sort of amalgam,” said Campbell, who includes – along with photographs of Christopher Robin and Graham in childhood – a quote from Shepard: “I also had a number of drawings I had made of Graham as a boy of six and these were very useful when, later on, I came to draw Christopher Robin.”

The close collaboration between Milne and Shepard – rare for an author and an illustrator at the time – is also explored, showing how Milne would ask Shepard for “more of this, or less of that” and their growing friendship. At first, Milne was not keen on Shepard as an illustrator – when Shepard started working for Punch, Milne had described him as “perfectly hopeless”. But their combination of text and illustrations proved irresistible. When We Were Very Young was published on 6 November 1925. The first print run of 5,140 copies sold out on publication day, with more than 40,000 printed by Methuen within eight weeks.

“Both Milne and Shepard and Methuen realised it was this combination of illustrations and narrative together that made it so compelling. It’s quite clear from the correspondence that they realised it was key to the success,” said Campbell. “As far as we are aware, these books were the first for children where the illustrations and the story were together. In children’s literature before – Alice in Wonderland, The Water Babies, Peter Pan – you see pages of text and then the illustrations dropped in.”

When the public called out for more, his publisher pushed Milne to write a book of prose stories featuring the teddy bear who had appeared in three of the poems in the first collection. US publisher John Macrae remembered that “during the process of bringing Winnie-the-Pooh into existence, I happened to be present at one of the meetings of Milne and Shepard – Milne sitting on the sofa reading the story, Christopher Robin sitting on the floor playing with the characters … and, by his side, on the floor, sat EH Shepard making sketches.”

Shepard would visit the Milnes’ country home in Sussex, where he was shown Ashdown Forest, inspiration for the Hundred Acre Wood. “There are images of Shepard going to the cottage … and being taken around so he could get the topography of the scenes right,” said Campbell.

When Winnie-the-Pooh was published in 1926, the first print run from Methuen was 32,000 copies. In the US, it had sold 150,000 copies by the end of the year, and has never been out of print since. Now We Are Six, the second collection of poems, would follow in 1927. The House At Pooh Corner was the fourth and final book.

“AA Milne wrote no more children’s literature, whereas Shepard continued to draw and to illustrate,” said Campbell. Technical innovations such as the introduction of colour printing meant he had to redraw some of the sketches, and editions in different languages also called for new images. “Essentially Shepard continued to draw Winnie-the-Pooh for the next 50 years, right up until the 1970s.”