In all likelihood he was already duke under Desiderius, notwithstanding some Frankish sources, such as the Einhardis annales, who say that Charlemagne put him in power after the Siege of Pavia.
It is likely that he had already become duke under Desiderius, although certain Frankish accounts, like the Einhard's Annals, suggest that Charlemagne installed him as ruler following the Siege of Pavia.