HISTORY OF ENGLAND BY DAVID HUME
( AN AUTHORITY ON THE SUBJECT)
https://ebooks.adelaide.edu.au/h/hume/david/history-of-england/chapter11.html
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Richard, when he entered on the holy war, declared his nephew Arthur, duke of Brittany, his successor; and by a formal deed he set aside, in his favor, the title of his brother John, who was younger than Godfrey, the father of that prince.
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the barons of the transmarine provinces Anjou, Maine, and Touraine, immediately declared in favor of Arthur’s title, and applied for assistance to the French monarch as their superior lord. Philip, who desired only an occasion to embarrass John, and dismember his dominions, embraced the cause of the young duke of Brittany, took him under his protection, and sent him to Paris to be educated along with his own son Lewis.
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Nothing enabled the king to bring this war to a happy issue so much as the selfish, intriguing character of Philip, who acted, in the provinces that had declared for Arthur, without any regard to the interests of that prince.
Constantia, seized with a violent jealousy that he intended to usurp the entire dominion of them, found means to carry off her son secretly from Paris: she put him into the hands of his uncle; restored the provinces which had adhered to the young prince; and made him do homage for the duchy of Brittany, which was regarded as a rere-fief of Normandy.
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Young Arthur, fond of military renown, had broken into Poictou at the head of a small army; and passing near Mirebeau, he heard that his grandmother, Queen Eleanor, who had always opposed his interests, was lodged in that place and was protected by a weak garrison and ruinous fortifications.
He immediately determined to lay siege to the fortress, and make himself master of her person; but John, roused from his indolence by so pressing an occasion, collected an army of English and Brabançons, and advanced from Normandy with hasty marches to the relief of the queen mother.
He fell on Arthur’s camp, before that prince was aware of the danger; dispersed his army; took him prisoner together with the count de la Marche, Geoffrey de Lusignan, and the most considerable of the revolted barons, and returned in triumph to Normandy. Philip, who was lying before Arques, in that duchy, raised the siege and retired upon his approach. The greater part of the prisoners were sent over to England, but Arthur was shut up in the castle of Falaise.
The king had here a conference with his nephew; represented to him the folly of his pretensions; and required him to renounce the French alliance, which had encouraged him to live in a state of enmity with all his family; but the brave, though imprudent youth, rendered more haughty from misfortunes, maintained the justice of his cause; asserted his claim, not only to the French provinces, but to the crown of England; and, in his turn, required the king to restore the son of his elder brother to the possession of his inheritance; John, sensible, from these symptoms of spirit, that the young prince, though now a prisoner, might hereafter prove a dangerous enemy, determined to prevent all future peril by despatching his nephew; and Arthur was never more heard of.
The circumstances which attended this deed of darkness were, no doubt, carefully concealed by the actors, and are variously related by historians; but the most probable account is as follows:
The king, it is said, first proposed to William de la Braye, one of his servants, to despatch Arthur; but William replied that he was a gentleman, not a hangman; and he positively refused compliance.
Another instrument of murder was found, and was despatched with proper orders to Falaise; but Huber de Bourg, chamberlain to the king, and constable of the castle, feigning that he himself would execute the king’s mandate, sent back the assassin, spread the report that the young prince was dead, and publicly performed all the ceremonies of his interment; but finding that the Bretons vowed revenge for the murder, and that all the revolted barons persevered more obstinately in their rebellion, he thought it prudent to reveal the secret, and to inform the world that the duke of Brittany was still alive, and in his custody.
This discovery proved fatal to the young prince: John first removed him to the castle of Rouen; and coming in a boat, during the night time, to that place, commanded Arthur to be brought forth to him. The young prince, aware of his danger, and now more subdued by the continuance of his misfortunes, and by the approach of death, threw himself on his knees before hia uncle, and begged for mercy: but the barbarous tyrant, making no reply, stabbed him with his own hands; and fastening a stone to the dead body, threw it into the Seine.