The artist Rembrandt van Rijn (1606–1669) is a highly regarded master of the Dutch Golden Age, and consequently the subject of extensive international research. Museums worldwide give him pride of place in their collections. Given the artist’s established prominence it is therefore shocking that in the last fifty years researchers have been able to successfully challenge the status of hundreds of artworks previously considered authentic. Added now to these challenges is a small unsigned portrait of an old bearded man in the University of Pretoria Museums. In 2016 this painting formed part of a pilot study investigating the provenance and authenticity of the J. A. van Tilburg Collection, donated to the university in 1980. Although international experts had attributed the portrait to Rembrandt since the 1890s, this article presents contradictory research that raises significant issues regarding these authentication processes and highlights the current position of considered art experts in such processes. Exploring the provenance of the painting and using the conclusions drawn from technical analysis, we show it is clear the painting in the University of Pretoria collection is not a Rembrandt.