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.
Upon his father's passing, Bernard became the target of discontent among some Alemannian aristocrats. In 890, he led a rebellion against Arnulf of Carinthia and prevented him from entering Italy as ordered by Pope Stephen V. Bernard had the support of Count Ulrich of Linzgau and Argengau, and was also backed by Abbot Bernard of Saint Gall. It is probable that he fled Alemannia for Italy in search of protection from Arnulf's rival, King Guy, as recorded by the late medieval historian Gobelinus.