He first appeared in 1961 as a short, fat, quiet man whose bad clothes “hung about his squat frame like skin on a shrunken toad”.

But that unassuming bespectacled man, with his deep love of the lesser German poets, was far from ordinary; he was George Smiley, one of the greatest, cleverest spies in fiction.

This autumn, his creator, John le Carré, will revive his finest and most-loved character for the final time in his new novel, A Legacy of Spies, with the writer making a rare public appearance to answer questions about all things Smiley.

Details were announced on Thursday of what will be, for many, the literary event of the year. An Evening with George Smiley will take place at Royal Festival Hall in London and be broadcast live to cinemas.

Le Carré, 85, said: “I am thrilled by the opportunity to discuss Smiley’s life and times with such a large and discerning audience, whether they know him from my books or from the screen; whether they are sitting in the Royal Festival Hall, or in a cinema in Britain or abroad.

“I hope that, between us all, we shall have an entertaining evening with George Smiley while simultaneously supporting MSF [Médecins Sans Frontières] – Doctors Without Borders – to whom the event is dedicated.”

Smiley’s first appearance, where he was tasked with unravelling an East German spy ring, came in Le Carré’s debut novel, Call for the Dead. He later appeared pulling the strings in The Spy Who Came in from the Cold before his most famous outing in Tinker Tailor Soldier Spy, later dramatised by the BBC with Alec Guinness and made into a film in 2011 with Gary Oldman as Smiley.

Gary Oldman in Tinker Tailor Soldier Spy. Photograph: Allstar/Focus Features

In total, Smiley has appeared in eight Le Carré novels, including a diversion from espionage in the more straightforward whodunnit A Murder of Quality.

Le Carré said he and Smiley “grew up together, despite the difference in our ages”.

“He appeared on the first page of my first novel, and he has been my secret sharer ever since,” he said. “When he became too celebrated for his own good, I went off and wrote other books, but he was always there, waiting for me, when I came back: not as Alec Guinness or Gary Oldman, but still my own Smiley with his own voice and his own loneliness.

“And so it was, when I decided to give him his final curtain in A Legacy of Spies.”

Le Carré, whose real name is David Cornwell, makes few public appearances; when he headlined at Hay festival in 2013, it was one of the event’s hottest tickets.

There was delight for fans when he made a cameo appearance in the BBC’s adaptation of his novel The Night Manager, as a smartly dressed restaurant diner incredulous at a drunken lobster salad incident.

Le Carré’s new novel will see Smiley and his colleagues from the Circus – his name for MI6 – return.

Few details are known about the book, although its publisher, Viking, has disclosed that it will feature Smiley’s protege Peter Guillam, who has retired from espionage and is living on the family farm in Brittany. He receives a letter from the secret service summoning him back to London because “his cold war past has come back to claim him”.

When the book was announced in March, it surprised many, particularly since Le Carré had said “I think I’ve done him” after Smiley’s last appearance in The Secret Pilgrim in 1990.

Le Carre’s agent, Jonny Geller, told the Guardian it was written in “a fever” over the previous 12 months.

“When I received the draft, I had to keep starting it again and pinching myself that I was in the company of all these great characters from the Circus. It really is going to be one of his finest, if not his finest, novel,” he said.

• John le Carré, An Evening with George Smiley, takes place on 7 September. Tickets are on sale on 8 May.