In 1536 the dauphin died, and Catherine’s husband became heir to the throne of France.  Though they had been married three years, no offspring had resulted, which unfortunate circumstance made her position a most uncertain one, especially as Diana of Poitiers was then at the height of her power, controlling Henry absolutely.  A furious rivalry sprang up between the Duchesse d’Etampes, mistress of Francis I., and Diana and Catherine; the two mistresses formed two parties, and a war of slanders, calumnies, and unpleasant epigrams ensued.  Queen Eleanor, the second wife of Francis I., took no active part, thus leaving all power in the hands of the mistress of her husband. (It was at this time that the Emperor Charles V. gained the Duchesse d’Etampes over to his cause.) Poets and artists, politicians and men of genius took sides, extolling the beauty of the one they championed.  Catherine, although befriended and treated with apparent respect by Diana, remained a good friend to both women, thus evincing her tact.  By keeping her own personality in the background, she won the esteem of both her husband and the king.

Brantome leaves a picture of Catherine at this time:  “She was a fine and ample figure; very majestic, yet agreeable and very gentle when necessary; beautiful and gracious in appearance, her face fair and her throat white and full, very white in body likewise....  Moreover, she dressed superbly, always having some pretty innovation.  In brief, she had beauties fitted to inspire love.  She laughed readily, her disposition was jovial, and she liked to jest.”  M. Saint-Amand continues:  “The artistic elegance that surrounded her whole person, the tranquil and benevolent expression of her countenance, the good taste of her dress, the exquisite distinction of her manners, all contributed to her charm.  And then she was so humble in the presence of her husband!  She so carefully avoided whatever might have the semblance of reproach!  She closed her eyes with such complaisance!  Henry told himself that it would be difficult to find another woman so well-disposed, another wife so faithful to her duties, another princess so accomplished in point of instruction and intelligence.  The menage a trois (household of three) was continued, therefore, and if the dauphin loved his mistress, he certainly had a friendship for his wife.  And, on her part, whenever she felt an inclination to complain of her lot, Catherine bethought herself that if she quitted her position she would probably find no refuge but the cloister, and that—­taking it all around—­the court of France (in spite of the humiliations and vexations one might experience there) was an abode more desirable than a convent;” this, then, is the secret of her submission.  In spite of her beauty, mildness, and distinction of manner, she could not overcome the prestige of Diana.