When Courtin arrived in London the French influence seemed ruined at Whitehall. Every night Charles visited the fascinating Duchesse, and every day on repairing to the Duchess of York, his sister-in-law, who was ill at the time, he found the enchantress at her bedside. Nevertheless Courtin paid his court to the new favourite and studied her every action. "I saw Madame de Mazarin at High Mass at the chapel of the Portuguese ambassador, who is dying of love for her," he wrote to Louis, "but could not help noticing that she betrayed disgust at the length of the service." The conversion of England to Catholicism, no less than the French influence, seemed doomed by the sway of the fair agnostic. Her position was so important that Courtin advised Louis to force the Duc de Mazarin to accede to her demand that he should allow her fifty thousand a year of the Cardinal's fortune, send her her jewels, laces, and precious furniture, and swear never more to molest her if she returned to France. The great Louis humbled himself to plead with her; even the Abbé de St. Réal, who still hung about her and talked of Charles like an aggrieved husband, was not neglected. Courtin promised him the favour of the French Court.
But suddenly in the heyday of her triumph the fears and hopes that the Duchesse had raised to such a pitch were dashed by the Duchesse herself. She was not equal to the position; none of the Mancinis had the ambition or political instinct of their famous uncle, the Cardinal. Pleasure, not power, was what Madame de Mazarin really craved. Never had the enemies of the Duchess of Portsmouth leant on a weaker reed. As usual the Duchess let her heart get the better of her head; she flung herself, cost what it might, into the arms of the dashing Prince of Monaco, who was on a two months' visit to the English Court and stayed two years for sake of La Belle Mazarin. Her political _rôle_ was over, and perhaps to no one connected with this intrigue did it give greater relief than to the protagonist herself. St. Réal, who had got together for his light-hearted mistress a good library, including such works as Appian and Tacitus, eaten up with jealousy, took the violent resolution of leaving England in the hope that she would call him back at Dover. But, as Forneron says, "she bore his absence with Roman fortitude and perhaps, like Louvois, who had perused some of his letters seized in the post, thought his room more agreeable than his company."