Marie-Charlotte-Constance Say, heir to the Say sugar refineries, was the last private owner of the Château from 1875 to 1938. Heading up one of the largest fortunes in France, she bought the Château in March 1875 at just 17 years of age, and married Prince Henri-Amédée de Broglie in June of that year. The princely couple made a great many changes to the Château to make it worthy of the grandest receptions. They installed running water, electricity and stove-based under-floor central heating. Visual pleasures and refinement also went hand in hand. The “Historical” apartments were filled with furniture from the 15th to the 19th centuries, the grand staircase was decorated with heraldic stained-glass windows, the dining-room was given a sumptuous neo-gothic fireplace, and the walls of the grand salon were covered in yellow silk brocatelle. Finally, particular attention was paid to the decoration of the council chamber, which was given back its original function as a reception room. Its floor was also laid with beautiful, decorative Majolica tiling, which was acquired from a palazzo in Sicily.
Many European and Eastern sovereigns were welcomed at Chaumont (Edward VII of England, Don Carlos of Portugal, Charles I of Romania), the Maharajas of Kapurthala, Baroda and Patiala, and artists such as Francis Poulenc, Francis Planté, Marguerite Deval and Sarah Bernhardt.
In 1905, Crosnier, director of the Say sugar factories, made some bad investments. His reckless speculations lost the de Broglie family a third of their fortune and only the scrupulous administration of the prince allowed them to keep up appearances. After his death in 1917, Princess de Broglie managed her fortune most carelessly, on top of which the Wall Street Crash of 1929 brought about currency devaluation. In September 1930, at 73 years of age, she remarried, with His Royal Highness Louis-Ferdinand of Orléans and Bourbon, Infante of Spain, who was just 42 at the time. Princess de Broglie thus became Princess of Orléans and Bourbon.
Following a number of financial setbacks, Princess of Orléans and Bourbon divided up the Domain of Chaumont, reducing it from 2 500 hectares to 21 hectares, sold off her multiple properties across the world and parted with thousands of works of art.
In 1937, the French State launched an expropriation procedure in the public interest and took possession of the Domain on 1st August 1938, as well as the sumptuous collection of tapestries and various pieces of furniture of a “historical nature”. Princess of Orléans and Bourbon spent her final days in two luxury hotels (the Ritz and the Georges V) and her Parisian flat on rue de Grenelle, where she passed away on 15th July 1943 at 86 years of age.
After having been a national monument, the Domain became regional in 2007.