"I opened it and there was this gorgeous painting. I got such a fright that I jumped and shut the portfolio again," she said. "I then took the painting out and couldn't stop looking at it - the colours, the vibrancy, it is such a beautiful piece of work. I couldn't believe it was there."
Wilson died with Captain Robert Falcon Scott and three others on their return from the South Pole in 1912.
Born in 1872, Wilson is much celebrated in his hometown of Cheltenham, England.
Cheltenham's art gallery and museum is named The Wilson and has a permanent collection of his work. His bronze statue, designed by Scott's widow Lady Kathleen Scott, stands outside the town's municipal buildings. A primary school in Paddington, London also bears his name.
The painting is labelled 1899 Tree Creeper and has the initial "T" on it. It depicts a tree creeper bird.
It was found in September, but has been kept confidential until now to allow the team to focus on restoring all of the 1500 artefacts from Cape Adare.
It wasn't immediately clear who the artist was, given that two expeditions had based themselves at Cape Adare, said the trust's programme manager for artefact conservation, Lizzie Meek.
"The Cape Adare huts were built by Norwegian Carsten Borchgrevink's expedition in 1899 and later used by Captain Scott's party in 1911. We knew the artist was likely to be among the men on those expeditions," she said.
As the trust worked to identify the artist, Bergmark-Jimenez attended a lecture at Canterbury University on Wilson.
"The presenter showed some of Dr Wilson's artwork. As soon as I saw his distinctive handwriting, I knew he had painted the Tree Creeper. This made sense as there was also a 1911 newspaper article from the Lyttelton Times in the papers and Scott's party went to Antarctica via New Zealand."
Meek said Wilson was a remarkable man.
"He was not only a talented painter, but a scientist and a medical doctor who was an integral member of both of Scott's expeditions to the ice."
Bergmark-Jimenez is not surprised the painting survived in such excellent condition.
"Watercolour paintings are particularly susceptible to light so the fact this work has spent more than 100 years tightly packed between other sheets of paper in completely dark and cold conditions is actually an ideal way to store it."
Meek said how the painting came to be in the hut is still a mystery.
"It's likely that Wilson painted it while he was recovering from tuberculosis in Europe. Clearly, he could have taken the painting to Antarctica on either of Scott's expeditions but we think it's more likely the artwork travelled with him in 1911, and somehow made its way from Cape Evans to Cape Adare."
The trust's permit to collect artefacts stipulates that all of the items must be returned to the site following conservation, in accordance with the site's status as an Antarctic Specially Protected Area (ASPA). This will happen once the huts have been restored.
Finding the painting is a poignant reminder of the inspiring legacy the early polar explorers left behind, said general manager of communications and operations Francesca Eathorne.
"More than a century later we are still sharing stories about those expeditions. We've been able to create a high quality facsimile of the painting so we are now looking forward to sharing it with the rest of the world. We are in no doubt this will attract global interest - particularly from our friends in the UK."
