Lucian Freud’s final painting in his series depicting benefits supervisor Sue Tilley is estimated to fetch up to £35m at auction – although the subject admits that she has “never got any money” herself. Sleeping by the Lion Carpet, which was painted from 1995 to 1996, will go up for sale at Sotheby’s for the first time in June. It has been hailed as one of the late artist’s defining masterpieces, with art critic and historian Martin Gayford calling it “the most important [work] that Freud has ever painted”.The painting depicts Tilley as she’s slouched on a leather sofa fully naked, with the subject sitting for Freud, who died aged 88 in 2011, three times a week over nine months. Speaking about how the painting is worth up to £35m, an amused Tilley told BBC Radio 4’s Today: “I’ve worked it out and I think I must be worth about £100m with the four paintings and all the etchings, and I think, ‘How can that be possible when I’ve never got any money myself?’” Sue Tilley in front of Sleeping by the Lion Carpet (PA)Tilley – who was in her late thirties when the work was painted – said that sitting for Freud was a “very pleasurable” experience.“What could be better? Lying around, being fed glorious food, being in the company of one of the greatest artists in the world and having all the Sunday supplements to read?” she said. Tilley joked: “I sometimes used to say, ‘Can you make my hair look a bit nicer, please?’, but he wouldn’t.”She also revealed that people often don’t recognise her even when she walks past the famous painting. Tilley recently went to see Freud’s paintings of her at the National Portrait Gallery, but believes people at the venue failed to spot her because her hair is now grey.Speaking to The Press Association, she added that the paintings show “all those skinny girls that big girls can do well as well”. “I feel like I’m an example for big women to show themselves off,” she said. “It’s good that it’s different. If everyone looked the same, it’d be boring, wouldn’t it?“That’s what I’m like and that’s what you have to accept, that all humans are different. Everyone’s got different things about them and they should be championed rather than brushed under the carpet.”Tilley, who is also known as “Big Sue” and later became an artist and writer, was paid just £33 a day by Freud to sit for his paintings after being introduced to the artist by their mutual friend, fashion designer Leigh Bowery. The works became a series of four large canvases, painted between 1993 and 1996. Lucian Freud painted Sue Tilley when she was in her 30s (AP)Sotheby’s has estimated the worth of the painting to be between £25m to £35m and will be exhibiting the artwork from 10 June as part of its London Modern and Contemporary Sales. In 2015, four years after Freud’s death, his 1995 portrait of Tilley, Benefits Supervisor Resting, broke records after it was sold for £35.9m. According to BBC News, Tilley found Freud fascinating to work with, revealing that he could be “mean, extremely generous, grumpy, funny, loud, quiet” – and later revealed that he dropped her as a friend after taking offence at an offhand remark she made. The only momentos of the art that Freud gave her were etchings of the portraits, however she sold them when she was short on money. Tilley later retired from the Job Centre and moved to East Sussex, where she began painting herself.