I'm no plant expert, but looking it up on Wikipedia, this one according to Dutch wiki could be Passiflora morifolia, but that doesn't exist in English wiki. In both Dutch and English however we can find the Passiflora caerulea (Common or Blue Passion Flower).
Thanks! It's not the morifolia (no berries on this one), but the second one looks close. (why on earth the neighbors/parents calls the thing "Clematis" then, I don't know..)
(why on earth the neighbors/parents calls the thing "Clematis" then, I don't know..)