A third portrait of Charlotte Bront has been discovered after being hidden away for almost 150 years.

The picture recently surfaced from a family collection. The owners, who have loaned it to the Bront Parsonage Museum, in Haworth, wish to remain anonymous. They had brought it in so the museum could check its authenticity.

But curator Rachel Terry is certain the circular chalk portrait, which measures just 12cm across, is the real thing.

She said: "I am always cautious when new images of the Bronts turn up. But this one does appear to be genuine."

Before it fell into the hands of the family collectors it belonged to William Law, a well-known private collector of Bront artefacts, whose family had it for around 100 years. But its authenticity is further sealed by the inscription on the back, which reads "Portrait of Charlotte Bront, given to Martha Brown 1855."

Martha, a servant to the Bront family, was given a number of items after Charlotte's death in 1855.

The only other known pictures of Charlotte are a painting by her brother, Branwell, of the three sisters in their teens and a chalk portrait by George Richmond after she had become a successful author.

The latest find will go on display from tomorrow when the museum re-opens for the new season.

Meanwhile, another painting by Branwell has returned to the museum a century after it was last on display there. The oil portrait, which dates from about 1839, depicts John Feather, who it is believed was a butcher in Haworth.