François Guillaume de Castelnau participated in the Papal conclave, 1523. Despite his youth (he was forty-three), he was the senior Cardinal priest at the Conclave. He and two French colleagues, Louis de Bourbon de Vendome and Jean de Lorraine, arrived thirty-six days late, on November 6, 1523, missing in addition the nine days of mourning for Adrian VI ("Novendiales"), and, more importantly, the political discussions that took place during that critical time and the forming of various alliances. The Cardinals who were present, however, were in no hurry. Although the Conclave began on 1 October, they did not complete their Electoral Capitulations until October 5. Voting finally began on 8 October, though during the first two weeks there were only eight Scrutinies. By 25 October voting positions had frozen, and, though votes continued to be taken, there were repeatedly the same results. On 12 November a delegation of Roman gentlemen appeared at the gate of the Conclave and exhorted the Cardinals to get on with their business and elect a pope. On the night of the 17/18 November, the deadlock finally broke, when Cardinal de'Medici threatened to nominate Cardinal Pompeo Colonna's worst enemy, Cardinal Franciotto Orsini. Rather than see that happen, Colonna and his followers joined the faction of Cardinal de'Medici and elected him pope. He chose the name Clement VII, and was crowned at the Vatican Basilica on 26 November 1523. The new Pope named Cardinal de Castenal bishop of Frascati in December 1523, the vacancy having been created by the promotion of Cardinal Alessandro Farnese to the Bishopric of Palestrina. Being the senior cardinal-priest, Cardinal de Castelnau had the first option on the office.