In October 1267, Conrad met his cousin, Conradin, at
Verona while the latter was preparing his advance into Sicily. He performed the
act of homage to Conradin and offered his services. In return, Conradin issued a charter confirming to Conrad all the fiefs he had held under Manfred and granting him the new title Prince of Abruzzo (
princeps Aprutii). In November,
Henry of Castile, the
senator of Rome and leader of the pro-Staufer
Ghibelline party in Rome, arrested the leaders of the pro-Angevin
Guelph faction and had them imprisoned in Saracinesco under the watch of Conrad's mother, Margherita, and wife, Beatrice. In response to this, on 25 April 1268, Clement IV issued the bull
Die coena Domini, excommunicating Conradin and his followers, including Conrad of Antioch. Conrad followed Conradin to Rome, where his entry on 24 July 1268 was greeted with festivities put on by the Ghibellines. When Conradin's army entered Sicilian territory a few days later, Conrad was leading a contingent of Tuscan militia. He was captured at the
Battle of Tagliacozzo (23 August) along with Conradin. The latter was executed by Charles on 29 August, but Conrad, who was imprisoned in
Palestrina, was spared through the intercession of Cardinal Giovanni Gaetano Orsini (the future Pope
Nicholas III), whose two brothers, Napoleone and Matteo, were among the prisoners being held by Conrad's wife. Finally, in the middle of September, the two brothers were released and in exchange Conrad was transferred to papal custody. ==Imprisonment and Papal fealty==