Edward IV had actually been born in France. His mother, Cecily Neville, had accompanied her husband as far as Rouen, which was safely under English control at the time.
This was during the tumultuous 1440s, when both England and France laid claim to the French throne. As Henry VI's Lieutenant of France, Richard, Duke of York, was stationed there for many years.
Three of his children, Edward, Edmund and Elizabeth, were all born in Rouen.
But then Louis XI's exclamations could merely be ignored as him causing trouble after the fact. After all, he had the nick-name of 'Universal Spider' for his scheming ways, and well knew the power of rumor. Plus it had been his father, Charles VII, who Richard of York had been trying to keep from becoming Dauphin.
Maybe Louis was worried that Edward IV would one day take up that cause again. It was a fair concern, because Edward did just that a few years later. Only Louis wasn't the only one stating such rumors.
Dominic Mancini, the Italian ambassador to England during 1482-3, dutifully noted down court gossip dating from twenty-two years earlier, when Edward had married his queen, Elizabeth Woodville. Mancini (who didn't speak English and was reliant upon the translations of Italian speakers at court) heard tell that Cecily Neville...
'...fell into such a frenzy, that she offered to submit to a public enquiry and asserted that Edward was not the offspring of her husband the Duke of York, but was conceived in adultery, and therefore in no wise worthy of the honor of kingship.'
If it was true, then no public enquiry occurred. Yet, even in England, the rumors persisted. Edward IV was forced to put out official rebuttals.
The story was always the same. Cecily Neville had fallen for a tall archer named Blaybourne, who was based at the English garrison in Rouen. She had become pregnant by the commoner, while her husband was away on campaign.
Richard, Duke of York, had claimed the baby as his son, solely to save his wife's blushes and assuage his own humiliation. If words were spoken, then they were behind closed doors. At the very most, all that was really compromised was the Duchy of York.
Of course, no-one could have imagined, in April 1442, that the newborn Edward would one day become King of England.