Jeff served as a military pilot with the Belgian Group of the Royal Airforce. He saw action during D-Day and downed a German bomber on that day in 1944. Together with his twin brother Alfred Jeff offered his services as a pilot to the British Royal air force in 1940, when Belgium was once again occupied by the Germans.
He successfully trained as a Spitfire pilot and served with 349 Squadron that mainly consisted of Belgian pilots.
To pay tribute to the last Belgian fighter pilot to serve in the Second world War the Belgian Air Force staged a fly-past of Strombeek-Bever (Grimbergen), Jeff’s home village, on Friday, the day of his funeral.