Secret sexy drawings by Branwell Brontë will be revealed at the first exhibition ever to focus exclusively on the wayward brother of the three literary sisters.

“Sex Drugs and Literature — the infernal world of Branwell Brontë” charts the tragic and sometimes scandalous life of the man who died a drunken wreck, aged 31.

It is to be launched next Saturday, at the Parsonage Museum, in Haworth, and will run until June 1, 2011.

It reveals the hidden decadent side of his life, both at his home at the parsonage and when working away for two short periods.

Research for the exhibition has unearthed faintly drawn indecent pencil sketches of figures on the back of a finished drawing.

It also charts his failed affairs and possible fathering of an illegitimate child.

The exhibition has been put together by the Brontë 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. It’s a scrawled and ill-spelled note and very sad when you consider what expectations they had for him.”

Branwell would illustrate some of his letters with drawings showing himself as a corpse or a drunken man, she added.

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. There was also a scandalous story that during employment in the Lake District he had an affair with a servant girl and fathered a child.

And he failed to hold down paid work, being sacked as a railway clerk for the Leeds and Manchester Railway. “You can see that as the girls went on to pen these fantastic novels, he ended up a sad alcoholic who achieved nothing,” said Mrs Dinsdale. Much of the archive about Branwell had come from the HH Houston collection, which had been donated by the American collection in the early years of the last century, she added.

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