"If I had known it was Saint-Exupery I would never have shot him down," Horst Rippert, 88, told AFP, adding that the Frenchman had been one of his favourite authors.
Rippert said he had been flying a Messerschmitt Me-109 over the Mediterranean near Toulon on July 31, 1944, when he spotted Saint-Exupery's twin-tailed Lightning.
"He was below me," Rippert said. "I saw his markings and manoeuvred myself behing him and shot him down."
Rippert, who scored 28 victories during the war, became a radio sports journalist after the war, said he only found out for sure recently who it was he had killed.
The former fighter pilot was tracked down by a French diver, Luc Vanrell, and the founder of an organization researching aircraft shot down during the war, Lino van Gartzen. The results of their findings are recounted in a book, "Saint-Exupery, the last secret," to be published in French on March 20.
For many years mystery surrounded the disappearance of Saint-Exupery, 44, a pioneer aviator known for his books about flying and his children's fantasy "The Little Prince."
He was serving at the ripe age of 44 with a Free French air force reconnaissance squadron based in Corsica when he failed to return from a mission to prepare for the landing of the allies in southern France.
Two years after a bracelet belonging to him was found in a fisherman's net off Marseille in 1998, diver Vanrell found remains of the Lightning, which were brought to the surface and identified from its serial numbers.