One of the “most astonishing” and obscure watercolours by Dante Gabriel Rossetti will go on public display at the British Museum this week.

Painted in the late 1850’s, ‘The Death of Breuze Sans Pitié’ reveals a shockingly darker side of Rossetti’s oeuvre. As the founder of the Pre-Raphaelite Brotherhood, Rossetti is better known for his sensuous paintings of dazzlingly beautiful women.

It is quite different from what we’ve come to expect from Rossetti,” said Susannah Walker, the exhibition’s curator at the British Museum. “We expect lovers and beautiful women, a very dreamy aesthetic. This is a very unusual painting.”

The painting has hardly been seen since it was painted, perhaps due to its jarring portrayal of a scene from Thomas Malory’s Morte d’Arthur. Rossetti depicts the knight Sir Dinadan furiously stabbing Sir Breuse to rescue “the wofullest lady in the world,” who stands in the background with a noose around her neck.

It is an image you really have to stand back from in order to decipher the action. It is not immediate and it is not what you expect from Rossetti, but it is an object which really grows on you,” said Walker.

For decades the watercolour was only known from written descriptions. In his 1899 book, HC Marillier called it “one of the crudest and least successful of all Rossetti’s water-colours”.

The renowned Victorian writer even described the piece as having a “repulsive and unpleasant effect” with a “grotesque and strained” composition.

‘The Death of Breuze Sans Pitié’ was one of seven medieval-inspired watercolours painted by Rossetti. Five ended up in the Tate collection, while this more gruesome piece was sold separately in a New York auction in 1926. Until it appeared again in London in 1993, Rossetti’s masterpiece was essentially lost without a single photograph to document it.

Late art historian John Christian purchased the painting, which was offered to the nation after his death as part of the acceptance in lieu scheme. The scheme allows owners to offer artworks and collections to the nation to offset inheritance tax.

Christian amassed a vast collection of over 900 objects, championing pre-Raphaelite artists when they were out of fashion in the 1960s and 1970s. The British Museum’s display will also include highlights from the collection by Charles Haslewood Shannon, Benjamin Robert Haydon, Dorothy Hawksley and Kalman Kemeny.

Speaking about the upcoming display, Walker explained that “it is a major acquisition offering a huge insight into Victorian art and is a real treasure trove for anyone who wants to learn more deeply about printmaking and drawing and honing the craft of drawing.”

‘John Christian: collecting the last Romantics’ opens on Tuesday 3 September and runs until Tuesday 12 November 2019 at the British Museum.