Beatrice of Flanders was born in Bruges circa 1253/1254 as the daughter of Guy of Dampierre, Count of Flanders and his first wife Matilda of Béthune. She had seven full siblings and eight half-siblings – from her father’s second marriage to Isabelle of Luxembourg.
Beatrice married the 14-year-old Floris V, Count of Holland in 1269. Their marriage was part of a peace treaty between Holland and Flanders. The treaty initially demanded that Guy of Dampierre’s eldest daughter should marry Floris’ uncle and guardian, known as Floris de Voogd, but if he should die before his nephew, Floris himself would take his place as the groom. This came into force when Floris de Voogd unexpectedly died on 26 March 1258. Floris did end up marrying one of Guy’s daughters, just not the eldest, Margaret, but Beatrice. It is unclear why as Margaret was still unmarried, but she did end up marrying John I, Duke of Brabant in 1273.
Beatrice and Floris went on to have at least seven children together, though possibly as many as nine. One source states that six sons and one daughter are buried together under a single stone in Loosduinen. Only two of their children survived infancy, so if that source is correct, they had nine children. Their two surviving children were Margaret who was born circa 1280 and John who was born circa 1284. Margaret was engaged in 1281 to Alphonso, Earl of Chester, son and heir apparent of King Edward I of England, until Alfonso’s death in 1284. Margaret died sometime in the summer of 1295. John too made an English match, and he was married to Elizabeth of Rhuddlan, a daughter of King Edward I.
During the siege of Middelburg in 1290, Beatrice brought her six-year-old son to the city to boost morale, and the city managed to hold strong for several months.
Floris took his son to England in early 1291 to make his claim for the Scottish throne (through his descent from Ada of Huntingdon). He took his son John with him as his wedding treaty of 1285 determined he should be raised in England. In his absence, Beatrice acted as head of a regency council. His claim for the Scottish throne was unsuccessful.
Beatrice died just before her husband. She was probably ill for quite a while before her death on 23 March 1296. Her husband was brutally murdered in a conspiracy on 27 June 1296. They were both buried in Rijnsburg Abbey.1