In this letter, written from Frankfurt in November 1589 (where he had visited the Book Fair in September) the composer asked Moretus for news of the publication of the new chansons for five voices he had sent with Moretus' agent to Antwerp:"[je] delivray a vostre homme un livre de musicque de Chansons françois a cinque parties de moy composé ... Monsieur, je vous prie affectueusement de voloir donner ordre [de publier]" ("I deliver to your man a music book of French chansons for five voices composed by me ... Sir, I beg you to give orders to publish it").
The note made afterwards by Phalèse on the back of the same letter reads:"Ick Pieter Phalesius kenne ontfanghen te hebben 5 Musyckboeken van Sr Moretus met 5 liekens daer naer gesonden." ("I Pieter Phalèse declare to have received five music books from Seigneur Moretus with five songs sent to him.")
This strongly suggests that Phalèse carried out commissions for the Officina Plantiniana. After all, De Castro addressed his enquiry to Moretus, not to Phalèse who received the letter only after Moretus had granted permission for publication.
The importance of this letter for the De Castro research is heightened by its suggestion of the existence of a new, unknown volume with chansons of five voices, which seems not to have survived. Castro wrote,"Ce pendant ie vous envoye la lettre dedicatoire ensemble une chanson toute novelle laquelle vous prie jointdre avecque les autres, et la mettre apres une chanson qui commense Si quelque corps humain" ("In the mean time I send you the dedication letter, together with a brand new chanson which I pray you to join with the others, and to put it after the chanson which starts with 'Si quelque corps humain'.")This chanson, however, cannot be found in any of the preserved volumes, which makes us presume that it concerns a lost (or never printed?) volume.
Moreover, the letter discloses the person to whom De Castro intended to dedicate this volume:"Monsieur [Moretus] je vous prie affectueusement voloir donner ordre, car mon Prince le Prince de Cleves de Juliers etc. en est desia adverti lequel en est trescontent" ("Sir Moretus, I pray you with affection to give orders [for the publication], since my Prince, the Prince of Cleve, Julich, etc is informed about it already, and he is very happy about it".)
Obviously, De Castro dedicated this volume, now lost, to his new patron Johann Wilhelm of Julich-Cleve-Berg. The seemingly inexplicable fact that of all the Düsseldorf volumes preserved, not one is dedicated to De Castro's patron, is now solved.