He and the King of France were first cousins, sons of two sisters of the house of Savoy.

So Charles VIII was obliged to see him, and went to visit him in the castle where he lived more like prisoner than lord.

He found him half reclining on a couch, pale and emaciated, some said in consequence of luxurious living, others from the effects of a slow but deadly poison.
But whether or not the poor young man was desirous of pouring out a complaint to Charles, he did not dare say a word; for his uncle, Ludovico Sforza, never left the King of France for an instant.

But at the very moment when Charles VIII was getting up to go, the door opened, and a young woman appeared and threw herself at the king's feet; she was the wife of the unlucky John Galeazzo, and came to entreat his cousin to do nothing against her father Alfonso, nor against her brother Ferdinand.
At sight of her; Sforza scowled with an anxious and threatening aspect, far he knew not what impression might be produced on his ally by this scene.

But he was soon reassured; far Charles replied that he had advanced too far to draw back now, and that the glory of his name was at stake as well as the interests of his kingdom, and that these two motives were far too important to be sacrificed to any sentiment of pity he might feel, however real and deep it might be and was.