A young student has just struck literary gold, discovering four previously unknown stories written more than a century ago by Katherine Mansfield.

Any new material by Mansfield, who had a dramatic impact on short-story writing as an art form, is of interest. But this find is all the more exciting because it includes a story offering fascinating, autobiographical insight into one of the most painful chapters of her life – unrequited love, a marriage of convenience and a stillborn baby.

A Little Episode dates from 1909 and reveals the bitter disillusionment of a love triangle whose memory Mansfield tried to erase by destroying all her personal papers from that year – to the exasperation of biographers.

Now it will help to reconstruct an obscure period of her life – the story of a musician who abandoned her, having made her pregnant, and a teacher she abandoned in turn on their wedding day, eventually losing her baby.

The discovery – which also includes previously unknown photographs – was made by Chris Mourant, 23, a PhD student at King's College London. Although in the university's archives, the material had been overlooked until he spotted its significance.

Learning that the University of Edinburgh was to publish the first complete edition of Mansfield's fiction, he contacted Dr Gerri Kimber, senior lecturer at the University of Northampton and the edition's co-editor with Vincent O'Sullivan. They were just about to send the first volume to press.

"My jaw dropped," Dr Kimber said. "This all happened last Monday."

At the eleventh hour, she has included the new stories as an appendix.

Three are charming, children's fairy tales from 1908 and the fourth has "huge biographical significance", Dr Kimber said, describing it as "brilliant" and "unputdownable".

Such is Mansfield's popularity that she has never been out of print. Her best-known writings include The Garden Party, from 1922, with the classic "The Daughters of the Late Colonel", an exploration of genteel frustration.

A Little Episode, written when she was 20, is a 2,500-word story that clearly mirrors her own affairs with Garnet Trowell, a musician who got her pregnant and then rejected her, and George Bowden, a singing teacher whom she wed, to give herself a married name, rejecting him on their wedding night.

She returned briefly to Trowell, who kicked her out after discovering her marriage.

In the story, "Yvonne" (Mansfield), a "bruised, trembling soul", is deeply in love with "Jacques St Pierre" (Trowell), a musician with a "pouting, eager mouth", and is married to "Lord Mandeville" (Bowden), whom she despises as a "howling bore" and who fills her with an "intolerable disgust".

Dr Kimber said: "No true scholar wants to mix biography with fiction. But you have to in this case.

"You see the bitterness that she feels against Garnet… and their unborn child, as perceived in the callous portrayal of a musician called Jacques St Pierre."

Mourant found the material among documents relating to ADAM International Review, a 20th-century literary monthly. The Mansfield stories were given to its founding editor, Miron Grindea, by her close friend Ida Baker, in the 1960s.

Extract from Katherine Mansfield's newly discovered short story A Little Episode:

"She threw off her clothes, hastily, brushed out her long hair, and then suddenly looked at the wide, empty bed.

"A feeling of intolerable disgust came over her.

"By Lord Mandeville's pillow she saw a large bottle of eucalyptus and two clean handkerchiefs. From below in the hall she heard the sound of bolts being drawn – then the electric light switched off…