Bestselling writer Bernard Cornwell, author of hit historical series Sharpe and The Last Kingdom, has apologised to fans for not delivering a new book this year for the first time since 1980, after having “the year from hell”.

Cornwell, 80, said he had hoped to finish the 25th novel featuring British Napoleonic war hero Richard Sharpe, portrayed on TV by Sean Bean, this year, but it would now not be completed until 2025. The novel, Sharpe’s Storm, is listed for publication for 21 October next year.

On his Facebook page, Cornwell, who was born in London but now lives in the US, wrote: “For those of you who were looking forward to Sharpe’s Storm I want to provide a brief explanation.”

He said that 2024 had been “the year from hell” and added: “I won’t go into detail, but just say there have been too many surgical procedures, chemotherapy sessions, dentists and hospital visits, and those things play merry hell with a writing schedule.”

Last year, Cornwell’s wife Judy, 87, whom he married in 1980, was diagnosed with leukaemia.

He said that, although he had written about two-thirds of the new Sharpe novel by July, he hit a major snag and had written himself into a plot cul-de-sac. Cornwell, whose books have sold more than 20m copies worldwide, said: “Sharpe’s Storm was still on track for completion. I needed to write about five more chapters and all the necessary research was done, but then I hit a roadblock.

“I knew the events of Storm fell between Regiment and Siege and, reluctant as I am to re-read my books, I did glance through Sharpe’s Siege to check some facts and, to my horror, realised that the grand finale I had planned for Sharpe in Storm was impossible because it would overlap with events in Siege. He might be a peerless hero, but even Sharpe cannot be in two places at once.”

Cornwell said he would have asked his editor at publishers HarperCollins, Susan Watt, for help, but last week it was announced that she had died after a 60-year career in British publishing.

He wrote: “Normally I would have consulted my extraordinary editor at HarperCollins to ask whether I could get away with it, but Susan had just unexpectedly and tragically died, and I was left to conclude that she would have brusquely told me not to be an idiot and find another solution.

“I’m happy to say that I have found a solution which will make Storm a much better book, but that solution demands intensive research, new chapters and a monumental rewrite of the existing chapters.

“Sharpe will be freed of the two-body problem, and all will be well, but it cannot be well in time for delivery and publication this year. For that, I am sincerely sorry. I like the book, such as it is, and it certainly puts Sharpe through a monstrous ordeal, but it must wait for 2025, during which I promise to refuse any major Shakespearean role and will do my utmost to avoid doctors and, especially, dentists.”

The Shakespeare reference refers to time out Cornwell took from writing over the summer to play Prospero in The Tempest at the Cape Cod Shakespeare festival.

He said: “I knew, because I first played Prospero in 2016, that the role would take an immense amount of time; the part is long and not easy. I made an admittedly feeble effort to refuse and give the role to one of our professional actors, but the feeble effort was rejected and I had to first relearn the part and then give up day after day in rehearsals.

“I don’t regret it because I revel in being a member of a company composed of enthusiastic and talented young people, but that indulgence meant more time lost.

“I would also like to add that I am now 80 years old and, as the great George MacDonald Fraser once remarked to me, ‘you slow down at 80.’ I have.”