A letter penned by Vincent van Gogh is expected to fetch as much as $405,000 at auction next week, a sign the modern world is still fascinated by the outsider artist.

The letter is thought to be the only one jointly written by Van Gogh and fellow painter Paul Gauguin, and was written in late 1888, when the pair were living and working in the French city of Arles.

It’s written to another post-impressionist artist Emile Bernard, and mentions the duo’s frequency to brothels.

“We’ve made some excursions in the brothels, and it’s likely that we’ll eventually go there often to work,” Van Gogh wrote, after he outlined his first impressions of his friend.

“At the moment Gauguin has a canvas in progress of the same night cafe that I also painted, but with figures seen in the brothels. It promises to become a beautiful thing.”

The opening pages of Van Gogh and Gauguin’s letter, in French.

It’s well known Van Gogh, and in turn Gauguin, were frequent visitors to brothels.

Van Gogh even left his severed ear with one of his favourite ladies at a brothel, which he cut off during a fight with Gauguin the month after the letter was written.

University of Western Australia chief cultural officer Ted Snell said there were no new revelations in the letter, but that it showed the camaraderie between the two artists – at least, before the severed ear incident.

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“Don’t listen to Vincent,” Gauguin eventually writes on the latter pages of the correspondence.

“As you know he’s prone to admire and ditto to be indulgent.”

French artist Paul Gauguin boarded with Van Gogh in southern France. Photo: Getty

Professor Snell said the banter between the two was engaging, and indicated Van Gogh’s excitement to have his friend join him.

“We know that Vincent was thrilled that Gauguin was joining him and obviously he wished to show him the ‘high’ life of Arles, in the local brothel,” Professor Snell told The New Daily.

It was in Arles that Van Gogh painted some of his best-known works, including the Sunflower series.

It was also where his mental health took a serious turn for the worse.

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While he painted furiously in Arles, his condition deteriorated a couple of months after Gauguin joined him.

After their fateful fight that turned violent, Van Gogh checked himself in an institution for a year.

He took his own life the following year, in July 1890, aged 37.

It’s often trotted out that Van Gogh was “before his time”, and sold but a smattering of paintings while he was alive.

Despite his shortcomings in life, Professor Snell said it was Van Gogh’s commitment to art as a complete life purpose that still hooked people’s fascination with the Dutch painter today.

The artist painted Sunflowers while living in the south of France with Gauguin, as well as 300-odd other artworks. Photo: Getty

“There is an urgency in Vincent’s work that is about that supreme sense of living life and finding beauty and meaning, whether in a corn field, a blooming sunflower or a peasant’s hands,” Professor Snell said.

“His position as an outsider, someone providing insight that is unavailable to others, is also part of his allure I’m sure.”

The letter is due to be auctioned in Paris next week, where it’s expected to fetch between $200,000 and $400,000.