Complex sentence: Philippe Erlanger, "L'Étrange Mort de Henri IV" (1957, rev.1999), reveals Épernon's association with Ravaillac through his mistress and concludes that he, the King's mistress Henriette d'Entragues and Charlotte du Tillet engineered the successful assassination.
Split into simpler sentences: Philippe Erlanger, "L'Étrange Mort de Henri IV" (1957, rev.1999), reveals Épernon's association with Ravaillac through his mistress. He concludes that he, the King's mistress Henriette d'Entragues and Charlotte du Tillet planned the successful assassination.