After a previous but failed crusade, Louis IX of France had the desire to return to the Holy Land and in 1270 was able to do so. His youngest brother, Charles, who had become king of Sicily, persuaded him to sail first to Carthage and subdue the infidels there. Plague was raging in the city and the king caught it soon after his arrival and died on 25 August 1270. 
His son, Philippe III and his wife, Isabelle of Aragon had accompanied him and they brought his body back to France, travelling overland through Italy. In the course of the journey, Isabelle fell 
from her horse and died of her injuries at Cosenza at the end of January 1271, having never set foot in France as Queen. 
Three years later Philippe married again and his choice fell on Marie of Brabant, of whom he had heard good reports. The new Queen was only eighteen and Philippe soon came to love her dearly, much to the annoyance of his chamberlain Pierre de La Broce, who felt that his influence over the king was being undermined. In 1276 Philippe's eldest son Louis, aged nine, died suddenly after a mysterious illness. 
Pierre put it about that he had been poisoned by his stepmother, and for a while things looked very black for Marie until her brother the Duke of Brabant, sent a knight from his court to prove her innocence by combat in the approved style of those days. She was completely vindicated and her accuser was hanged. 
Philippe III died of malaria in October 1285, aged only forty. Marie, who had given him three children, survived for many years and died in the reign of her step-grandson, Philippe V, in 1321. 
 

Source: Leo van de Pas