Abraham van Helsing and his intrepid band of vampire hunters may have disposed of Bram Stoker's creation Dracula more than a century ago, but a sequel to the novel co-authored by Stoker's great-grand-nephew will see them under attack from the undead once again, it was announced yesterday.

Dacre Stoker, who formerly coached the Canadian Olympic pentathlon team and now lives in the US, delved into his ancestor's handwritten notes on the original Dracula novel to pen his sequel, Dracula: The Un-Dead - the original name of Dracula before an editor changed the title.

The new book - the first Dracula story to be fully authorised by the Stoker family since the 1931 film starring Béla Lugosi - has provoked a storm in the publishing world, selling for more than $1m (£575,000) to Dutton US, HarperCollins UK and Penguin Canada.

Dacre Stoker wrote the novel with the screenwriter Ian Holt, and a movie is also planned.

The new novel, which is due to be published next October, draws on excised characters and plot lines that were cut from Stoker's original, first published 111 years ago.

In the new book, set in London in 1912, Quincey, the son of Stoker's hero, Jonathan Harker, has become involved in a troubled theatre production of Dracula, directed and produced by Bram Stoker himself. The play plunges Quincey into the world of his parents' terrible secrets.

Stoker said that he had not got around to reading his great-grand-uncle's novel until he went to college. "Word got out about my family connection to the old vamp and I grew tired of being unable to answer people's questions. So I chose to finally break down and read the novel for a research paper on Bram and his possible motivations to write the story," he said.

"I had seen so many film versions of Dracula and was terribly surprised that very few of the films had any resemblance to Bram's original novel. Because the novel was so good and had stood up so well over the years, I found it exceedingly sad that all of the trash Hollywood had put out monumentally sullied Bram's and my family's literary legacy."

Stoker later met Holt and the pair decided to work together to resurrect Bram Stoker's original themes and characters. "Our intent is to give both Bram and Dracula back their dignity," Stoker said.

Bram Stoker's original Dracula has never been out of print since it was published in 1897.