One of Harper Lee’s surviving relatives says it’s possible there could be major unpublished works by the author still to be discovered, following the release of eight of her previously unseen short stories.

Describing the mystery around a manuscript titled The Long Goodbye, which Lee wrote before To Kill A Mockingbird, Lee’s nephew, Dr Edwin Conner, told Sky News: “Even the family doesn’t know everything that remains in her papers. So, it could be there waiting to be published.”

Dr Conner says Lee submitted a 111-page manuscript, titled The Long Goodbye, after writing Go Set A Watchman in 1957.

The retired English professor explains: “It’s not clear to me or to others in the family, to what extent [The Long Goodbye] might have been integrated into To Kill a Mockingbird, which she wrote immediately after, or to what extent it was a freestanding manuscript that is altogether different and that might stand to be published in the future.”

A second mystery exists in the form of a true crime novel, The Reverend, which Lee was known to have begun researching in the late 1970s, about Alabama preacher Reverend Willie Maxwell who was accused of five murders before being murdered himself.

Dr Conner said: “The manuscript of a nonfiction piece, that according to some people doesn’t exist, according to others who claim to have seen it, does [is also a mystery]. We don’t know where it is, or whether it is, really.

“That could be a surprise that has yet to be revealed if we discover it and it’s published, which is a real possibility.”

He believes much of the manuscript was written in his family home and says his mother, Louise, who was Lee’s older sister, saw a “finished version of it” on the dining room table.

Dr Conner says there are “others who just as fiercely say no, it was never completed”.

‘She did want to publish these stories’

There has long been debate over why Lee published just two books in her lifetime.

To Kill a Mockingbird came out in 1960. Selling more than 46 million copies worldwide, translated into more than 40 languages and winning a Pulitzer Prize, it’s arguably the most influential American book of the 20th century.

Fifty-five years later, Lee published a sequel, Go Set A Watchman, written ahead of Mockingbird, but set at a later date.

Then aged 88, and with failing health, there were questions over how much influence Lee had over the decision to publish.

Asked how happy she’d be to see some of her earliest work, containing early outlines for Mockingbird’s narrator Jean Louise Finch and the story’s hero Atticus Finch, now hitting the shelves, Dr Conner says: “I think she’d be delighted.”

He says Lee had presented them to her first agent, Maurice Crane, at their first meeting in 1956, “precisely because she did want to publish these stories”.

And while dubbing them “apprentice stories,” which he admits “don’t represent her at her best as a writer,” he says they show “literary genius of a kind”.

Notoriously private, he says the stories – which were discovered neatly typed out in one of Lee’s New York apartments after her death – offer “deeply enthralling new glimpses into her as a person”.

Never marrying or having children, he says Lee maintained a degree of privacy even with her family: “You never saw her complete personality… We thought we knew her, we thought we’d seen everything, but no, we hadn’t.”

‘That’s it, I’m not giving any more interviews’

While describing her as a “complicated woman,” he insists Lee was far from the recluse she’s frequently painted as.

He says: “In company, she was most of the time delightful. She was a lively personality, she was funny, witty, and you would think she was very outgoing.”

But Lee was known to have struggled with her success.

Dr Conner explains: “She never ever wanted fame or celebrity because she suspected, or knew, that would involve the kind of uncomfortable situations in public situations that she found just no satisfaction or pleasure in”.

He says while in the early years of Mockingbird Lee gave interviews, the wild success of the book soon rendered such promotion unnecessary, leading her to decide: “That’s it, I’m not giving any more interviews”.

While he admits she was subsequently much happier, he goes on: “Not that she was a recluse, as some people thought. She wasn’t at all a recluse, but she didn’t enjoy public appearances and interviews particularly. She wanted the work to speak for itself.”

‘Deeply hurt’ by Truman Capote

Famously close to Truman Capote, one of the pieces in Lee’s newly released collection is a profile of her fellow author.

Dr Conner says that piece – a love-letter of sorts, describing Capote’s literary achievements – is all the more remarkable because at the point Lee wrote it in 1966, when she and Capote “were not even on speaking terms”.

He says Lee “probably knew [Capote] better than any other person alive when that was written”, adding, “she did love him as a friend very much, even when he was not speaking to her”.

Friends since childhood – and the prototype for the character of Dill in Mockingbird – Capote later hired Lee to help him research his 1965 true crime novel In Cold Blood.

Despite his book’s relative success, Dr Conner believes Capote was “bitter” over the fact Mockingbird far eclipsed it in accolades and recognition.

“He had been writing for much longer. He felt that he was at least as good as she was, and he was very envious of her success”.

Dr Conner says Lee was “deeply hurt” at Capote’s rejection of her, never speaking about him in later life.

Recalling his own meeting with Capote many years later, Dr Conner says he “got a personal sense of how [Capote] could charm the socks off of anybody, male or female”.

He says it was noteworthy that while Capote asked about his mother, who he had been fond of, he “never once mentioned” Harper.

Sky News has contacted Lee’s lawyer and the executor of her estate, Tonya Carter, for comment.

The Land of Sweet Forever: Stories and Essays, by Harper Lee is on sale from Tuesday