 According to the same Spanish official letter from 30 June, William of Nassau's only son was taken prisoner in the Fort of Liefkenshoek and shot dead by his captors to prevent his rescue by a group of Dutch soldiers.The victory of Kallo was described by the Cardinal-Infante to King Philip as the ""greatest victory which your Majesty's arms have achieved since the war in the Low Countries began"", and by the Dutch as ""a great disaster"".The recapture of the key fortress of Kallo forced Frederick Henry to abort the whole offensive, which turned as one of the worst Dutch defeats of the war, thus undermining the reputation of the statholder.