They say you have to suffer for your art. Which might explain why Lucian Freud went straight to the studio when he was punched by an irritated taxi driver - but not for a lie down to recover.

A newly discovered self-portrait of Britain’s most famous – and bankable – living artist is going on sale next month which shows the artist sporting a black eye. Legend has it that the notoriously reclusive painter, widely considered to be Britain’s best living artist, decided to use his run-in with an angry taxi driver to compose an unusual self-portrait rather than wallow over an altercation that left him noticeably worse off than his adversary.

The composition begins just above the artist’s top lip and ends at a tousle of messy brown hair. But it is the angry swelling around Freud’s left eye that makes the portrait so unusual. It is only the third time a self-portrait of Freud, now 87, has become available through an auction and it is expected to fetch between £3m and £4m when Sotheby’s sells it next month.