After his father's death, Bernard became the focus of revolt for some Alemannian magnates. In 890, he rebelled against Arnulf of Carinthia and prevented the king from going into Italy as requested by Pope Stephen V. Bernard had the support of Count Ulrich of the Linzgau and Argengau and Bernard, Abbot of Saint Gall. Probably, he fled Alemannia for Italy and the protection of Arnulf's rival, King Guy, as recorded by the late medieval historian Gobelinus, who may have had a lost Carolingian work as his source.
Following his father's death, Bernard became a point of contention among some Alemannian nobles. In 890, he rebelled against Arnulf of Carinthia and blocked the king's attempt to enter Italy as commanded by Pope Stephen V. Bernard had the backing of Count Ulrich of Linzgau and Argengau, and was also supported by Abbot Bernard of Saint Gall. It is likely that he left Alemannia for Italy in search of protection from Arnulf's rival, King Guy, as documented by Gobelinus.