Provinces of Belgium
During the second half of the 20th century, Belgium transitioned from a unitary state to a federal state with three Communities and three Regions. As part of the state reforms, the (bilingual) province of Brabant was split in 1995 three ways: into two (unilingual) provinces (Flemish Brabant and Walloon Brabant) and into the (bilingual) Brussels-Capital Region. (The Brussels-Capital Region does not belong to any province, is not a province, and does not contain any provinces.) The two new Brabant provinces became part of the Flemish Region and the Walloon Region respectively. The remaining eight provinces became part of these regions as well, so the Flemish Region and the Walloon Region each contain five provinces.
History of Flanders
The contemporary territory of Flanders (i.e., the Flemish Region as the Dutch-speaking part of the Kingdom of Belgium) contains within it the core of the old county, West Flanders and East Flanders, plus three more provinces to the east which were not originally part of Flanders. These are the provinces of Antwerp and Flemish Brabant which were historically part of the Duchy of Brabant, and the province of Belgian Limburg, which was part of the Prince-Bishopric of Liège. (The city of Brussels, historically part of Brabant, is now politically part of the Flemish Community but not of the Flemish Region.)