The double life of an Irish speaking Professor in Donegal who was thought to be a Nazi spy has been unearthed for a new BBC documentary.
Dr Ludwig Mulhausen, a proud Nazi Party member and German linguist, was living in the small village of Teileann in the Donegal Gaeltacht.
In Nazi sa Ghaeltacht, veteran reporter Kevin Magee has now investigated claims he was scouting the village out as a possible location to launch an invasion of the Irish Free State.
The programme will show how Professor Mulhausen perfected his knowledge of the Irish language to broadcast German propaganda in Ireland.
As an Irish speaker himself, Kevin first heard stories of a Nazi spy after visiting the area over 40 years ago.
Mulhausen was said to have made no secret of his allegiance to the Nazis, and often berated locals for their lack of German efficiency.
Kevin said: "I wanted to find out if the story of the Nazi in the Gaeltacht was true, so I began investigating, talking to locals, asking questions and examining a whole variety of sources.
"Piece by piece I was able to pull this remarkable story together. When I began my journey, I had no idea I would discover just how committed Muhlhausen was to the entire Nazi project. The plot reads like a World War Two thriller, except this story is for real."
After hanging a large picture of Adolf Hitler on his bedroom wall, Mulhausen later took photographs everywhere and measured the depth of Teileann Bay by dropping lead weights.
Locals speculated that he was scouting the area as a potential landing site for Nazi vessels.
Two years after his visit, Teileann locals were shocked to hear him broadcasting propaganda in Irish from a Berlin radio station, urging the Free State to keep its neutrality and to remember the atrocities of the English.
In the hour-long documentary, Kevin brings the untold piece of Ulster wartime history to life with historians, locals and military experts.
Beginning in Donegal, he travels to Dublin to uncover a government file on Mulhausen, and on to Berlin to view previously unseen documents about Hitler's plans for Ireland after invasion.
Nazi sa Ghaeltacht is broadcast on Sunday, July 26, on BBC Two, 10pm.