The Nieuwe Kerk acquired its link with the House of Orange- Nassau more or less by chance. Shortly before his death, William of Orange had chosen Delft as his temporary residence, from where he led his fight against the Spanish occupier.. When he was assassinated there on 10 July 1584 at the Prinsenhof by Balthazar Gerards, the burial vaults of the were unreachable. For this reason the Prince was buried in the Nieuwe Kerk. Since then, the Nieuwe Kerk has been the last resting-place for the members of the Royal House.

http://www.nieuwekerk-delft.nl/eng/kerkgebouw/index.html