The French marksman who shot the British commander at Trafalgar is the hero of Le Chevalier de Saint Hermine, a 900-page work that Dumas was turning out for serial publication in the months before his death in 1870.

The imminent appearance of the lost Dumas, the product of eight years of detective work by Claude Schopp, a Dumas expert, had been kept secret and took the literary world by surprise yesterday.

M Schopp gathered the text from newspapers of the period and other places, including a library in Prague.

Britain has always doubted French claims that Sergeant Robert Guillemard, a Provençal fuselier, shot Nelson from the mizzen mast of Le Redoutable and survived to tell the tale.

Midshipman John Pollard was credited by Captain Thomas Hardy, commander of HMS Victory, with killing the sniper, who was described as an anonymous infantryman.

As an older man, the then Commander Pollard wrote to The Times in 1863 to complain that another former midshipman, Edward Collingwood, was trying to take the credit.

Dumas appears to have exploited uncertainty over the identity of the marksmen to put his hero’s finger on the trigger. By weaving historic fact with swashbuckling fiction, the author of The Three Musketeers was pursuing his life’s mission of bringing French history to the masses through fiction.

St Hermine is the long-missing third part of a trilogy about a band of aristocratic adventurers in the Revolutionary terror and the Napoleonic Empire. Hector de St Hermine appears briefly in the previous two parts, Les Blancs et les Bleus and Les Compagnons de Jehu.

Dumas sometimes used real figures as his central character. More often, he preferred to insert romantic, larger-than-life heroes into real events.

The Napoleonic period was especially dear to Dumas because he idealised his late father, the only mulatto general in Napoleon’s army.

M Schopp described his excitement on coming across episodes of St Hermine in 1869 editions of Le Moniteur Universel newspaper, while researching in a library. “For a quarter of an hour, handling this treasure, I felt as if I owned the world,” he told Le Figaro. It is great Dumas, in the same vein of the revenging hero as The Count of Monte Cristo.”

As well as repairing the syntax and narrative confusion in Dumas’s famously chaotic texts, M Schopp also added a hypothetical ending — in italics — to a book that lacked the final pages. An English- language version is due soon.

Dumas scholars have long known of Le Chevalier de St Hermine, but with 95 novels and a big inventory of plays to work on, none had set about unearthing the final work.

Jean-Pierre Sicre, the head of Phebus, which is publishing the novel, said that it was especially interesting because Dumas was its sole author. Dumas was known for employing a stable of hack writers. He used his spare time to spend his fortune and indulge his appetites for women and swashbuckling.

AUTHOR'S TALE

• Born 1802 near Paris
• Married actress Ida Ferrier in 1840 but soon separated, after having spent her dowry
• Famous for The Three Musketeers and The Count of Monte Cristo, written 1844-45
• Participated in 1830 revolution in Paris and 1860 Italian struggle for independence
• Died of a stroke near Dieppe in 1870

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