A hitherto unknown portrait believed to be of author Emily Bronte is expected to fetch thousands of pounds when it goes under the hammer this week. The oil painting is the latest in a flurry of items relating to the Bronte sisters to be put up for auction in the last few months. Its sale by JP Humbert\'s in Northamptonshire comes after the auction house sold another painting of the reclusive writer for £23,836 in December. Auctioneer Jonathan Humbert said the 33 by 24cm (13 x 9.5 ins) painting has already attracted international interest after the previous sale - which originally had a guide price of £10,000-£15,000. The second painting, which is annotated \"Emily Jane Bronte\", was originally estimated to fetch around £3,000 but, after growing interest, now has an estimate of £5,000-£8,000 for its sale on Thursday. Mr Humbert said: \"This painting is softer and less formal than the previous \'Bonnet Portrait\' and importantly, the artist has entitled the painting \'Emily Jane Bronte\' on the bottom left hand side of the picture at the time of painting. \"Clearly the picture is mid-19th century so we can draw a sensible conclusion that Emily Bronte was quite possibly the sitter. \"One unknown portrait of Emily Bronte is luck enough but two in two months is quite remarkable. \"Sadly the signature of the artist on the lower right is barely decipherable. \"We are certainly offering it as a painting of Emily Bronte - the art world is apt to be scornful of \'undiscovered\' works but a painting like this really gets people talking and debating. We have received interest already from the USA and Canada.\" The painting will go under the hammer on Thursday evening at JP Humbert\'s saleroom in Towcester. In December an unpublished manuscript by sibling Charlotte Bronte was sold at auction to a Paris museum for a record value of £690,850 at Sotheby\'s. Sotheby\'s estimated it would sell for between £200,000 and £300,000, but the manuscript sold for more than double the top estimate, setting new auction records for a manuscript by Charlotte Bronte and for a literary work by any of the Bronte sisters. It was bought by Paris museum La Musie des Lettres et Manuscrits, scuppering attempts by the Bronte Society to return it to the Bronte Parsonage Museum at the writer\'s home in Haworth, West Yorkshire. From The telegraph