In 1975, Francis Bacon made a startling (and typically shocking) painting of himself and his lover George Dyer, who had taken his own life in 1971, observed by a dwarf-like voyeur.

He later cut the painting in two – the "dwarf" half is now, reputedly in a private collection in Australia but the 6-feet-high, vertical format half of the painting depicting Two Figures is to go on sale at Christie's in London on February 11th.

The estimate is £5 million-£7 million.

The painting is being sold by Michael Peppiatt, a friend and confidant of the artist and a curator and biographer of his work.

The Daily Telegraph said Peppiatt's ownership was "one of the art world's best kept secrets" until now and that "now in his mid-70s" he's decided to sell "mainly, he says, because he can't afford to live with it". Insuring a Bacon painting is expensive.

When he received it in the 1970s, paintings by Bacon could be bought for under £100,000.

Commenting on the painting, Christie's said: "Two Figures consummates one of the darkest self-reflective periods of Bacon's life: a period defined not only by an intensive, highly analytical stream of self-portraiture, but also by the landmark series of four 'black' triptychs, in which he sought to exorcise the painful memories of Dyer's suicide."