Triangular UFO appears in the sky over Amsterdam

This triangle shaped object was sighted near Amsterdam in Wormeveer, Netherlands. The film-maker discovered it to the east outside the village. Since it was windy he first thought at a kite. But it looked larger on the sky and it looked like made of some sort of metal. Also a string was not seen. The object did absolutely not move like a kite. As afterwards the object suddenly flew away lightning fast the film-maker was scared.