In June 1879, Royal MS 16 E VIII, a unique 13th-century manuscript, vanished from the Round Reading Room of the British Museum after being returned by a Prussian reader. This essay synthesises 20 years of rigorous research since the author’s previous publications, offering new insights into this significant case.The study examines the intense academic rivalries between German and French scholars after the Franco-Prussian War and the profound cultural significance of Royal MS 16 E VIII, which contained the sole copy of "Le Voyage de Charlemagne a Jerusalem et a Constantinople, " believed to be the oldest poem in French literature. It highlights key figures, including the Prussian philologist Eduard Koschwitz and Herr Rothe, J.R.R. Tolkien’s teacher at KES, and provides a detailed textual reconstruction of the lost manuscript.Aimed at historians, philologists, and medievalists, this updated work illuminates the impact of the Franco-Prussian War on academic nationalism and cultural heritage. It is an indispensable resource for understanding a pivotal moment in the history of Europe and the British Museum.