A long-lost memoir has revealed how an Irish soldier saved a young Adolf Hitler and fought on both sides during World War I.

The story of Dubliner Michael Keogh began when he joined the British Army in 1914 and won the George's Cross for bravery before he was captured by the Germans in 1916.

While in captivity, he was persuaded by pro-German Irish members of the Roger Casement Brigade, a group created to recruit Irish soldiers to fight against the British, to join them.

He joined a Bavarian regiment and met Hitler in September 1918 near Ligny on the French border because they were both in the same regiment.

The memoir of his life disappeared as he lay on his deathbed in Dublin  in 1964.

According to his son Kevin (84), who lives in  Dublin, a man "dressed as a priest" took them from under his pillow two days before he died.

The files were  found in the UCD archives and given back to the family in 2004.

The memoirs report how Keogh saved a young Adolf Hitler’s life in a move  that changed the course of history.

After the war Keogh stayed on in Munich in the army to fight against the Communist rulers who had declared a short-lived Bavarian Soviet Republic in April 1919.

In his memoirs he describes how, as the officer on duty during the anti-Communist revolution, he received an urgent call about a riot involving 200 men and two "political agents," one of them being Hitler, in a nearby gym.

"I ordered out a sergeant and six men and, with fixed bayonets, led them off on the double."

Keogh recounts that the two political agents, who had been speaking from a table top, had been dragged to the floor and were being beaten.

"The two on the floor were in danger of being kicked to death. I ordered the guard to fire one round over the heads of the rioters. It stopped the commotion."

The soldiers managed to free the two injured politicians.

"The crowd around muttered and growled, boiling for blood," he added.

"The fellow with the mustache gave his name promptly: Adolf Hitler.

"They had come to the barracks as political agents for the new National Socialist German Workers' Party."

Keogh says he has no doubt he had saved the future Fuerher’s life.