According to a letter written in 1390, Guillem Nicolau attached a full commentary to his Catalan translation of Ovid’s Heroides. Although these glosses have not survived in any of the extant manuscripts of this translation, they have been preserved in a fifteenth-century manuscript containing an anonymous Castilian version of the Catalan text. In this article, the linguistic- and literary-based identification of these Castilian glosses with those written by Nicolau leads to a further examination of the relationship of the Catalan Heroides to the Latin commentary tradition. Evidence is given of Nicolau having used a Latin manuscript containing accessus and glosses from William of Orléans Bursarii Ovidianorum, as well as many other grammatical and contextual anonymous glosses, to which he is heavily indebted.