聖イシュトヴァーンの王冠
He was then crowned with the Holy Crown of Hungary in Székesfehérvár by the Bishops of Veszprém and Csanád on 6 December. However, Otto was not able to strengthen his rule. In the course of 1306, Otto's second opponent Charles of Anjou occupied Esztergom, Szepes Castle, Zólyom and some other fortresses in the northern parts of the kingdom, and in the next year he also occupied Buda. In June 1307, Duke Otto III visited the powerful Voivode of Transylvania, Ladislaus Kán, but the latter imprisoned him. On 10 October 1307, the magnates presented at the assembly in Rákos proclaimed Charles king, but the most powerful aristocrats (Matthew III Csák, Amadé Aba and Ladislaus Kán) ignored him as well. At the end of the year, Ladislaus Kán set Otto free who then left the country, but the Voivode of Transylvania still denied to hand over the Holy Crown of Hungary to Charles, whose legitimacy could be questioned without the coronation with the Holy Crown.