In 1773, Pierre Sandelin, Comte de Fruges, purchased the former Hôtel du Gouverneur de Saint-Omer. The old hotel had fallen into disrepair, and it was decided to demolish it and rebuild a new residence in its place. But Pierre Sandelin died in 1776, so it was his wife, Marie-Josèphe, who brought the project to fruition. The mansion follows the French model of the hotel “between courtyard and garden”. Since 1955, the building has been listed as a Monument Historique because of the rarity, exemplarity and integrity of the premises. It is one of the finest examples of 18th-century civil architecture in the Nord-Pas-de-Calais region.