AbstractAmadís de Gaula (AG) and its sequel Sergas de Esplandián (SE) are masterpieces of medieval Spanish chivalric romances. Much debate has been devoted to the role played by their purported author Garci Rodríguez de Montalvo. According to the prologue of AG, which consists of four books, the author allegedly revised the first three books that were in circulation at that time and added the fourth book and SE. However, the extent to which Montalvo edited the materials at hand to compose the extant works has yet to be explored extensively. To address this question, we applied stylometric techniques for the first time. Specifically, we investigated the stylistic differences (if any) between the first three books of AG and his own extensions. Literary style is represented as usage of parts-of-speech n-grams. We performed principal component analysis and k-means to demonstrate that Montalvo’s retouching on the first book was minimal, while revising the second and third books in such a way that they came to moderately resemble his authentic creation, that is, the fourth book and SE. Our findings empirically corroborate suppositions formulated from philological viewpoints.