De la Colonilla's children were not interested in the estate and sold it to Alexandre Aguado, the Marquis de Las Marismas, a true Spaniard, unlike De la Colonilla! At that time, Aguado was the first banker to purchase a great Bordeaux château. His fortune, which he owed as much to finance as to grand public works, was already immense, and Château Margaux did not constitute for him a means of expanding it, but rather a pleasant place in which to live.

 
He abandoned his financial activities quite quickly in order to become, among other things, the patron of Rossini, who went on to compose a zarzuela called ... ''Château Margaux'' ! He died rather young in 1836, leaving his magnificent collection of Italian and Spanish paintings to the Louvre museum. His essential legacy was the Napoléon decoration which remained in its original state until the estate was sold by the Ginestet family to André Mentzelopoulos.

 
The fortunes and misfortunes of the 19th century contrasted with the perennity of the vineyard, which remained remarkably well maintained by successive estate managers, even though disaster appeared in the form of a fungus from the United States called powdery mildew, which caused terrible damage to the vines before sulphur came to the rescue. This cryptogamic disease was only the beginnning of a series of catastrophes that were to follow, and the sulphur antidote was the first spray treatment in the history of the Bordeaux vineyard.

In 1879, Emily Macdonnel, a Scottish lady-in-waiting of the Empress Eugénie and the wife of the son of Aguado, sold the château to the count Pillet-Will.