Marie Valentine Joséphine de Sainte-Aldegonde, Duchess of Dino (29 May 1820 – 23 September 1891) was the wife of Alexandre Edmond de Talleyrand-Périgord, 3rd Duke of Dino, and mistress of Anatoly Nikolaievich Demidov, 1st Prince of San Donato.
He offered her a diamond ornament whose magnificence caused the bridegroom worry.
The next year, in 1840, Demidov briefly broke off their liaison due to financial problems, but later that same year married Princess Mathilde Bonaparte and resumed his affair with Valentine on his first stay in Paris after his wedding.
In 1845, he arranged for Valentine to settle with him in Florence and stayed by her side, even though her husband took umbrage.
At a costume ball, Valentine was insulted by her rival, Mathilde, and in response Demidov slapped his wife twice in public, which signalled their final separation soon thereafter.