The tears of his mother Elizabeth and the advice of Friar Robert, the old minister, who had fled to Buda, confirmed him in his projects of vengeance.

He had already lodged a bitter complaint at the court of Avignon that, while the inferior assassins had been punished, she who was above all others guilty had been shamefully let off scot free, and though still stained with her husband's blood, continued to live a life of debauchery and adultery.

The pope replied soothingly that, so far as it depended upon him, he would not be found slow to give satisfaction to a lawful grievance; but the accusation ought to be properly formulated and supported by proof; that no doubt Joan's conduct during and after her husband's death was blamable; but His Majesty must consider that the Church of Rome, which before all things seeks truth and justice, always proceeds with the utmost circumspection, and in so grave a matter more especially must not judge by appearances only.
Joan, frightened by the preparations for war, sent ambassadors to the Florentine Republic, to assert her innocence of the crime imputed to her by public opinion, and did not hesitate to send excuses even to the Hungarian court; but Andre's brother replied in a letter laconic and threatening:-- "Your former disorderly life, the arrogation to yourself of exclusive power, your neglect to punish your husband's murderers, your marriage to another husband, moreover your own excuses, are all sufficient proofs that you were an accomplice in the murder." Catherine would not be put out of heart by the King of Hungary's threats, and looking at the position of the queen and her son with a coolness that was never deceived, she was convinced that there was no other means of safety except a reconciliation with Charles, their mortal foe, which could only be brought about by giving him all he wanted.

It was one of two things: either he would help them to repulse the King of Hungary, and later on they would pay the cost when the dangers were less pressing, or he would be beaten himself, and thus they would at least have the pleasure of drawing him down with them in their own destruction.
The agreement was made in the gardens of Castel Nuovo, whither Charles had repaired on the invitation of the queen and her aunt.

To her cousin of Durazzo Joan accorded the title so much desired of Duke of Calabria, and Charles, feeling that he was hereby made heir to the kingdom, marched at once on Aquila, which town already was flying the Hungarian colours.