▁all ▁planned ▁celebr ations ▁in ▁Ap el do orn ▁were ▁cancel led . ▁Later ▁that ▁day , ▁many ▁other ▁events ▁across ▁the ▁Netherlands ▁were ▁also ▁cancel led , ▁short ened ▁or ▁ton ed ▁down ▁significantly ▁– ▁including ▁all ▁activities ▁in ▁Rot ter dam ▁and ▁many ▁events ▁in ▁Amsterdam . ▁ ▁As ▁the ▁news ▁of ▁the ▁attack ▁spread , ▁many ▁people ▁sp ont ane ously ▁lower ed ▁the ▁national ▁flag ▁to ▁half - m ast ▁( the ▁normal ▁flag ▁instruction ▁on ▁Queen ' s ▁Day ▁is ▁to ▁fly ▁the ▁flag , ▁with ▁orange ▁b anner , ▁normally , ▁and ▁many ▁people ▁follow ▁this ▁instruction ). ▁Prime ▁Minister ▁Jan ▁Peter ▁Bal ken ende ▁announced ▁the ▁order ▁to ▁lower ▁all ▁flags ▁on ▁government ▁buildings ▁to ▁half - m ast . ▁ ▁Initial ly , ▁it ▁was ▁fe ared ▁that ▁the ▁" act ▁of ▁mad ness ▁by ▁a ▁l one ▁attack er " ▁end anger ed ▁the ▁long - h eld ▁year ly ▁tradition ▁of ▁the ▁royal ▁family ' s ▁m ing ling ▁with ▁the ▁Dutch ▁people ▁on ▁Queen ' s ▁Day . ▁ ▁Memorial ▁service ▁On ▁ 8 ▁May , ▁a ▁mem orial ▁service ▁was ▁held ▁in ▁the ▁Or phe us ▁theatre ▁in ▁Ap el do orn , ▁with ▁speech es ▁by ▁Prime ▁Minister ▁Jan ▁Peter ▁Bal ken ende ▁and ▁mayor ▁of ▁Ap el do orn ▁Fred ▁de ▁Gra af . ▁It ▁was ▁attended ▁by ▁the ▁Queen , ▁the ▁Prince ▁of ▁Orange , ▁Princess ▁M á xim a , ▁Princess ▁Marg ri et ▁and ▁Pi eter