Video report by ITV News Arts Editor Nina Nannar
For many years a drawing by Lucien Freud remained hidden away, with its existence only known to the nun who owned it.
But now the sketch is being sold to help fund a pony centre which the revered artist loved to visit.
Freud began visiting the Wormwood Scrubs Pony Centre in west London in 2003 – eight years before he died in July 2011 – to paint the horses there.
One of his sketches, of a horse called Goldy, was left unfinished and passed on to Sister Mary-Joy – who initially had no idea who he was.
“I turned to him and said ‘could you just remind me what your name is please?’ and we had a youngster here who was an art student and she was behind him,” she told ITV News.
“And she was horrified that I hadn’t a clue who this gentleman was.”
The artist decided he didn’t like Goldy’s personality, she says, moving onto Sue, another horse, which resulted in one of his most famous works.
Sister Mary-Joy now wants to fund improvements to the centre on its 30th birthday and is selling the unwanted sketch to finance them.
"It could raise very little or it could go sky high, with a little bit of luck," she said.
"I think he would be delighted."
The auction takes place in December.