The problem with fact-based fiction

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The problem with fact-based fiction is ... well ... facts. They can really mess up a good story.

I'd read that the Mortemarts, the family of Athénaïs, Madame de Montespan, lived on rue de Rosiers.

Perfect: rue des Rosiers is not far from where Claude des Oeillets, my main character, lived when she first came to Paris. It worked into the story perfectly. Their lives do become entwined; nobody knows how their relationship began, but as a novelist it helped that they were walking distance from o...