Things came to a head in autumn 1246, when Kaliman of Bulgaria died, leaving the country in the hands of a regency for his younger brother Michael Asen (). Vatatzes quickly attacked Bulgaria, and within three months captured most of Thrace and all of eastern and northern Macedonia, while Michael II of Epirus also took advantage of the opportunity to expand into Albania and northwestern Macedonia. At the close of this campaign in November, as Vatatzes was encamped at Melnik, he was informed of a conspiracy to depose Demetrios and deliver Thessalonica to him in exchange for a chrysobull guaranteeing the traditional rights and privileges of the city. Vatatzes readily granted this, and sent envoys to Demetrios calling for him to appear in person at his camp. Demetrios, suspicious of Vatatzes' intentions, refused, and the Nicaeans marched on Thessalonica. After a few days, the conspirators opened one of the gates to the Nicaean army, and the city was quickly captured. Demetrios was captured and exiled to Lentiana in Bithynia, while Thessalonica and all of Macedonia were placed under the governance of the Grand Domestic Andronikos Palaiologos. Theodore himself, isolated and without power in his refuge at Vodena, apparently remained uninvolved in these events.