Pope Formosus
Lambert was crowned King in May 891 at Pavia and joint Emperor alongside his father on 30 April 892 at Ravenna by a reluctant Pope Formosus. He and his father signed a pact with the pontiff confirming the Donation of Pepin and subsequent Carolingian gifts to the papacy. In 893, however, Formosus sent an embassy to Regensburg to request Arnulf of Carinthia liberate Italy and come to Rome to be crowned. Arnulf sent his son Zwentibold with a Bavarian army to join with Berengar of Friuli. They defeated Guy, but bribes, along with an outbreak of fever, saw him leave in the autumn. Arnulf then personally led an army across the Alps early in 894. He conquered all of the territory north of the Po River, but went no further before Guy died suddenly in late autumn. Lambert became sole king and emperor, as well as succeeded his father to the Duchy of Spoleto. Still young though, he was left under the regency of his mother, a staunch anti-German. While Berengar occupied Pavia, Lambert and Ageltrude travelled to Rome to receive papal confirmation of his imperial title, but Pope Formosus wanted instead to crown Arnulf and was imprisoned in the Castel Sant'Angelo.