The Guardian has a nice backstory to Bonhams latest Irma Stern find:

In the late 50s, the painting was given by the collector Betty Suzman – sister-in-law of the anti-apartheid activist and politician Janet Suzman – to a charity auction to raise funds for Nelson Mandela and other African National Congress activists, including Walter Sisulu and Oliver Tambo, who were on trial for high treasonand faced the death penalty. […]

Giles Peppiatt, director of Bonhams South African art department, said: “This painting was a significant part of Mandela’s defence fund – there were other works of art given to the auction, but they were very minor. This was by far the most important piece.”

The heavy, ornate frame that protected the painting in pristine condition during its noticeboard years is itself a rare and valuable thing, made from the timbers of elaborately carved antique door cases from Zanzibar, which are now barred from export. […] The parents of the present owner emigrated tothe UK in the 70s, bringing their auction prize painting with them.

“The words ‘shocked’ and ‘astonished’ wouldboth apply to the present owners,” Peppiatt said.“They loved the painting and they knew it hadsome value, but they had no idea it was such animportant work. In some ways they are very sorryto see it go, but it would be a great luxury to keepa million-pound painting hanging on a kitchen

South African painting discovered in use as a kitchen noticeboard valued at £1m (The Guardian)