A historically significant painting by the prominent South African artist Irma Stern was being used as a notice board when it was rediscovered in a London flat. Arab in Black (1939) was sold in the early 1960s by Betty Suzman, the sister-in-law of the anti-apartheid activist Helen Suzman, to help cover the legal costs of Nelson Mandela and his 155 co-defendants on trial for high treason. Stern also donated a work to benefit the Treason Trial Defence Fund, though she worried that offering more would attract attention from the authorities. “I was undertaking a routine valuation when I spotted this masterpiece hanging in the kitchen covered in letters, postcards and bills,” said Hannah O’Leary, the head of South African Art at Bonhams. “It was a hugely exciting find even before I learned of its political significance.” The work is expected to sell for between £700,000 and £1m.