Secret sexy drawings by Branwell Bronte will be revealed at the first exhibition to focus exclusively on the Bronte sisters’ wayward brother.

‘Sex, Drugs and Literature – the infernal world of Branwell Bronte’ charts the tragic and sometimes scandalous life of the man who died a drunken wreck aged 31. It is to be unveiled on Saturday, May 30, at the Parsonage Museum in Haworth and will run until June 1, 2011.

Research for the exhibition has unearthed faintly-drawn indecent pencil sketches of figures on the back of a finished drawing. The exhibition also charts his failed affairs and possible fathering of an illegitimate child.

It has been put together by the Bronte Parsonage Museum’s collections manager, Ann Dinsdale, and her staff.

She said: “On the back of a finished drawing there are small figures that look like scenes of decadence. We think that Branwell might have been in the habit of making sketches of indecent behaviour and this one has survived – other artists have done the same.

“He was a tragic failure in many ways. His father and sisters had great expectations of him but they never materialised and he died an alcoholic and addicted to opium. Perhaps one of the most pathetic episodes was a last note to his friend John Brown, who lived in the village, written just before he died asking him if he could get hold of five pence worth of gin.”

As his sisters worked on their novels, Branwell failed to hold down the profession as a portrait painter in Bradford and was dismissed in disgrace from a job as a tutor after an alleged affair with his boss’s wife.

“He ended up a sad alcoholic who achieved nothing,” said Mrs Dinsdale.

Branwell died in September 1848 followed by Emily, 30, in December and Anne, 29, in May 1849. Charlotte died in March 1855, aged 38.