His predecessor was Gomelo II and he first appears in a document of the latter's episcopate, on 20 January 905, signing as both a presbyter and a primicerius ("Flacinus presbyter, Primicerius testis").
According to a later falsified document of bishop Pelagius of Oviedo, Alfonso III held a council at Oviedo in 899 or 900 and with the approval of a certain "Pope John" (perhaps John VIII was intended) raised Oviedo to metropolitan rank.
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Only one document from his episcopate survives, though it was interfered with at a later date by Pelagius of Oviedo.