A scenario well known to Beowulf scholars alleges that after Beowulf has slain the monsters and gone home, Hrothulf, nephew of the Danish king Hrothgar, will murder prince Hrethric to gain the throne when the old king dies. This story, that many Anglo-Saxonists assume is integral to the ancient legend of these kings, is a modern misreading of the poet's allusions to events associated with the Scylding dynasty — a legendary history that the poet arguably takes care to follow. The present essay, in two parts, first shows how the idea of Hrothulf's treachery arose and became canonical under the influence of prestigious English and American scholars, then finds fault with this idea, refuting its “proof” from Saxo Grammaticus and showing how some Anglo-Saxonists have doubted that Beowulf supports an interpretation making Hrothulf a murderer. But when the poet's allusions to future treachery are ambiguous, at least for modern readers, in order to exonerate Hrothulf fully one must go to traditions about the Scylding dynasty outside the poem. Scandinavian regnal lists (including one that Saxo himself incorporates) consistently contradict the event the Saxo passage has been used to prove, as they agree on a sequence of Scylding rulers with names corresponding to those of persons in Beowulf. Attention to this traditional sequence exposes Hrothulf's murder of Hrethric as a logical impossibility. Moreover, the early medieval method of selecting rulers suggests that neither did Hrothulf usurp the throne of Denmark. In sum, careful scrutiny of the best Scandinavian evidence and rejection of the worst reveals Beowulf's “treacherous Hrothulf” to be a scholarly fantasy.