I'll come back with some data on his diagnosis. Maybe good to add the following: we believe that his gluten intolerance occurred before he was diagnosed with diabetes, because the intestinal check showed that it was quite damaged already. Apparently in many cases the sequence is the opposite: first diabetes, followed by gluten intolerance.
Regarding the diet: strictly gluten free, we eat little bread, predominantly baked at home, but pasta daily. Also, we substituted cow milk with goat milk, right from the start. Lots of veggies, fruit and salad (hard in the beginning, but he likes it now). Fish and meat intake has probably increased as the carb intake in a GF diet tends to be less.
We also stimulated physical exercise, right from the start.