The Queen and the Courtesan — Freda Lightfoot

Henriette d'Entragues isn't satisfied with simply being the mistress of Henry IV of France; she wants a crown too. Despite his promises to marry her, the King is obliged by political necessity to ally himself with a rich Italian princess. But Henriette isn't one for giving up easily. All she has to do to achieve her ambition is to give Henry a son, and then do whatever it takes to set him on the throne...