The wartime broadcasts of Grand Duchess Charlotte of Luxembourg were beacons of hope to her beleaguered people during the dark days of World War II, but it took a chance meeting on a Somerset railway station to bring her story to the cinema screen.

When the Nazis invaded neutral Luxembourg on May 10 1940 the royal family and the Government fled to raise awareness of the people's plight among the Allies.

The Nazis regarded the little state as German territory, ordered the population to speak German, deported Jews to concentration camps, and ordered young Luxembourgers to serve in the German Army or Labour camps.

Gustav Simon, the Nazi-appointed Gauleiter reported directly to Hitler and after a General Strike in 1942 instituted a reign of terror which saw thousands arrested, tortured, killed or sent to camps.

As families feared every knock on the door, and men went into hiding rather than fight for the enemy, one calm voice borne over the airwaves kept hope alive. Broadcasting via the BBC's World Service the Grand Duchess Charlotte became a "propagandist in pearls", telling the population the whole world knew of their suffering and there was no doubt of the final outcome.

Producer Candice Allen, remembered her grandmother, a Luxembourger, telling her how much those broadcasts meant. In a chance meeting on Castle Cary railway station she told film producer Lynn Rothwell that she had always wanted to retell the story on film.

Now together with Ray Tostevin, of Yeovil-based Grace Productions, they have brought the story to the screen in a feature-length documentary which has had an international British Academy of Film and Television Arts premiere in London.

Charlotte, a Royal at War, narrated by actress Geraldine James, includes interviews with Luxembourgers who remember how she spoke: "Like a mother and a wife."

The Grand Duchess also carried out propaganda tours and broadcasts from the United States, winning a pledge from President Roosevelt that the US would liberate the Duchy. His eldest grandson, Curtis Roosevelt, speaks in the film of the terrible toll the liberation took of American lives –with 19,000 killed in the Battle of the Bulge, and 70,000 injured or missing. The film has brought an unexpected bonus for Mr Tostevin, who wrote and directed the film, and for producers Candice Allen and Lynn Rothwell.

Grand Duke Henri, Luxembourg's current head of state, and grandson of Grand Duchess Charlotte, has awarded each the 'Chevalier de l'Ordre de Mérite Civil et Militaire d'Adolphe de Nassau', which translated means 'Knight of the Order of Civil and Military Merit of Adolph of Nassau'.

Mr Tostevin said: "The award is a great honour. But there are many others in Grace's production team who've worked equally hard to help pull-off this feature length history documentary film.

"After being so well received by cinema audiences in Luxembourg, we're now looking to secure acquisitions from broadcasters here in Britain and internationally."