I made some additional progress on “The Sun King” which is a popularized history of Louis XIV and his court. There was excitement a-plenty as the police decided the time was right to crack down on poisoners who were apparently doing great business getting rid of unwanted wives, husbands and relations for the upper class.
They caught and executed a few, but then the prisoners started to name Marquise de Montespan the mistress of Louis and mother of his eldest son, though not a legitimate heir. Rumors said that she had attended at least one Black Mass and used that, and spells, and chemicals to keep the king. The story also says that when requested to attend another, she could not fit it into her schedule, which has a ring of truth to it.
Even though he had already cooled to her physically, this was too close to home to be allowed out in open court, and further trials were quashed to avoid embarrassment. The accused did avoid execution, but were scattered across the country and forbidden to discuss the matter with anyone.
This last sounds a lot like the “Man in the Iron Mask”.