Sue Tilley, a 60-something retired benefits supervisor, is the subject of Lucian Freud's monumental 1996 painting, "Sleeping by the Lion Carpet." This artwork is set to go to auction at Sotheby's as part of the Lewis Collection sale on June 24. Sotheby’s Europe chairman Olivier Barker has called it Freud's "magnum opus," with an estimated value between £25 and £35 million ($33-45 million).

Tilley, also known as "Big Sue," was paid £33 a day by Freud to sit for him three times a week over nine months, resulting in a series of four large canvases between 1993 and 1996. Despite the substantial valuations of these paintings, Tilley has never directly profited from the sales. She humorous states, "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?’". She also mentioned selling the etchings Freud gave her when she needed money, using the proceeds for a holiday.

Two of Freud’s earlier portraits of Tilley have already broken records: "Benefits Supervisor Resting" (1995) sold for £35.9 million in 2015, and "Benefits Supervisor Sleeping" (1995) sold for $33.6 million in 2008, setting a record for a living artist at the time. "Sleeping by the Lion Carpet," painted between 1995 and 1996, depicts Tilley fully naked, slouched on a leather sofa. It is considered one of Freud's defining masterpieces and will be exhibited from June 10 to June 23 at Sotheby’s in London.

Tilley expresses hope that the painting will convey a message that "big girls can do well" and encourages people to appreciate Freud as a "marvellous painter" who observed humans authentically. She finds it surreal to see her youthful image auctioned for such vast sums. The painting is part of a larger collection from British billionaire Joe Lewis, with the entire sale expected to exceed £150 million ($201 million), making it the "most valuable collection ever offered in the UK."