The occasion was as follows.
A certain dispensation had been granted some time before to a nun who had taken the vows: she was the only surviving heir to the throne of Portugal, and by means of the dispensation she had been wedded to the natural son of the last king.

This marriage was more prejudicial than can easily be imagined to the interests of Ferdinand and Isabella of Spain; so they sent ambassadors to Alexander to lodge a complaint against a proceeding of this nature, especially as it happened at the very moment when an alliance was to be formed between the house of Aragon and the Holy See.

Alexander understood the complaint, and resolved that all should be set right.

So he denied all knowledge of the papal brief though he had as a fact received 60,000 ducats for signing it--and accused the Archbishop of Cosenza, secretary for apostolic briefs, of having granted a false dispensation.

By reason of this accusation, the archbishop was taken to the castle of Sant' Angelo, and a suit was begun.
But as it was no easy task to prove an accusation of this nature, especially if the archbishop should persist in maintaining that the dispensation was really granted by the pope, it was resolved to employ a trick with him which could not fail to succeed.