John I of France

WI: He survives and reigns for many years and has at least one son who succeeds him. Could this possibly prevent the outbreak of the Hundred years war, since it weakens Edward III of England's claim to the French crown? John I was born in 1316, and was close in age to Edward.
 
Sure it'd stop the 100 years war. But it won't prevent the English from fighting the French. Whether or not the English claim the French throne, there's a long-running dispute over the sovereignty of the English duchies in France. That series of wars won't end until either the English are kicked off the continent and struggle to return, or the English win so decisively that the French are prevented from making war on them again until a point at which they've essentially be seen to have waited too long.
 
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