In 965, Count Arnulf the Great of Flanders died, leaving a small child as his only heir. In the wake of his death, the West Frankish King Lothar annexed his southern lands for the crown. This paper examines how and why Lothar was able to succeed in this. By the 950s, the Flemish count was diplomatically isolated and facing threats to his southern border. Arnulf attempted to ally with Lothar to remedy this, basing his claim to alliance on their links of kinship via descent from Charles the Bald. Lothar supported Arnulf during his lifetime, but after his death sought to conquer part of his lands for himself. Moreover, he supported his own candidate for the Flemish regency, Arnulf’s nephew Baldwin Baldzo, over Arnulf’s candidate, his son-in-law Count Dirk ii of Holland, in order to cement his position as suzerain in northern Flanders. Lothar was able to do this by appropriating Arnulf’s claims to kinship with him and using them to justify his intervention in Flanders.