The accidentally found testament of Hieronymus Valvasor from 1602, a record of the last will of the polymath Johann Weikhard Valvasor’s grandfather, provides answers to several unresolved or partially resolved questions regarding himself and his nuclear family, and thus sheds light on subsequent developments in the Valvasor family. The most crucial discovery is that the founder of the Carniolan Valvasor lineage deliberately reinforced a lie concerning his origin by presenting himself as a blood relative of his noble benefactor Johann Baptista Va(l)vasor, who moved to Carniola from Bergamo and, in 1581, bequeathed Medija Castle to Hieronymus. At the same time, the last will offers a reliable insight into the private affairs, social ties, cultural environment, and linguistic practices in the family of a newly settled upstart of common descent and a noblewoman at the turn of the seventeenth century. Although not remarkably rich in its content, the document is of outstanding importance not only for being the last will of the most prominent ancestor of Johann Weikhard Valvasor and the founder of the Carniolan lineage of the Valvasor family, but also for depicting the social-material strategies and practices pursued by the emerging social elite.