Finally managed to get the brake line out of the caliper.
Lots of heat (I doubt that the caliper is painted, at least there is no sign of burned paint after the heat gun) but no way with a brake line wrench.
Had to cut the line and tried with a 10 nut. No way either (turned inside the nut).
Even more heat and a water pump plier did it.
Don't tell me this was the holy grail of brake lines!