The empress seemed to be deeply impressed by her nephew’s threatening attitude, and promised to do her best to persuade the queen to grant all he asked, on condition, however, that Charles should allow the necessary time for carrying through so delicate a business.  But Catherine profited by this delay to think out her own plan of revenge, and ensure the means of certain success.  After starting several projects eagerly and then regretfully abandoning them, she fixed upon an infernal and unheard-of scheme, which the mind would refuse to believe but for the unanimous testimony of historians.  Poor Agnes of Duras, Charles’s mother, had for some few days been suffering with an inexplicable weariness, a slow painful malady with which her son’s restlessness and violence may have had not a little to do.  The empress resolved that the first effect of her hatred was to fall upon this unhappy mother.  She summoned the Count of Terlizzi and Dona Cancha, his mistress, who by the queen’s orders had been attending Agnes since her illness began.  Catherine suggested to the young chamberwoman, who was at that time with child, that she should deceive the doctor by representing that certain signs of her own condition really belonged to the sick woman, so that he, deceived by the false indications, should be compelled to admit to Charles of Durazzo that his mother was guilty and dishonoured.  The Count of Terlizzi, who ever since he had taken part in the regicide trembled in fear of discovery, had nothing to oppose to the empress’s desire, and Dona Cancha, whose head was as light as her heart was corrupt, seized with a foolish gaiety on any chance of taking her revenge on the prudery of the only princess of the blood who led a pure life at a court that was renowned for its depravity.  Once assured that her accomplices would be prudent and obedient, Catherine began to spread abroad certain vague and dubious but terribly serious rumours, only needing proof, and soon after the cruel accusation was started it was repeated again and again in confidence, until it reached the ears of Charles.

At this amazing revelation the duke was seized with a fit of trembling.  He sent instantly for the doctor, and asked imperiously what was the cause of his mother’s malady.  The doctor turned pale and stammered; but when Charles grew threatening he admitted that he had certain grounds for suspecting that the duchess was enceinte, but as he might easily have been deceived the first time, he would make a second investigation before pronouncing his opinion in so serious a matter.  The next day, as the doctor came out of the bedroom, the duke met him, and interrogating him with an agonised gesture, could only judge by the silence that his fears were too well confirmed.  But the doctor, with excess of caution, declared that he would make a third trial.  Condemned criminals can suffer no worse than Charles in the long hours that passed before that fatal moment when he learned that his mother was indeed guilty.  On the third day the doctor stated on his soul and conscience that Agnes of Durazzo was pregnant.