Jean de Montagu

Jean de Montagu or Jean de Montaigu (ca. 1350 or 1363, Paris – Paris, 17 October 1409), was a royal secretary and pupil to Charles V, and subsequently an administrator and advisor to Charles VI of France, who became a leading figure in France during the early 15th Century. Charles V like his father before him, was Duke of Normandy at a young age. 
Biography.
Jean was the son of Gerard de Montaigu and Biette de Cassinel or Biota Cassinelli, called "la belle Italienne" ("the beautiful Italian woman"). She was the daughter of François Cassinel (died 1360), a sergeant in the Royal Army, and great-granddaughter of Bettino Cassinelli, who had immigrated from Italy to Paris. It was said that he was the illegitimate son of Charles V of France, but the Nineteenth Century author Merlet writes that Charles was 12 or 13 at the time of Jean's birth. Jean de Montagu had two brothers or half brothers: Gérard de Montagu the Younger (died 1420), who was bishop of Poitiers and bishop of Paris; and Jean de Montagu (killed 25 October 1415 at the Battle of Agincourt), who was bishop of Chartres, and archbishop of Sens.
He made a career at the royal court, rising to become Grand Treasurer and Grand Master of France. In 1389, Jean bought the lands of Boissy-sous-Saint-Yon and Égly for twelve hundred pounds.
Being the leading figure of the royal government during the period following the assassination of Louis, the Duke of Orléans, in the ongoing Armagnac-Burgundian Civil War, he developed a very bitter rivalry with the Duke of Burgundy, John the Fearless, who sought to hold the Regency (and the income of the Royal Household) in place of the mentally incapable King Charles, as his father had done.  
In 1409, John the Fearless had him arrested with the help of the Provost of Paris during one of King Charles' mad spells. The Queen and the Duke of Berry, among several others, pleaded for his release to no avail. After an expedited summary trial where he unsuccessfully appealed to the then Burgundian-controlled Parliament a forced confession of treason and other charges upon being subjected to torture, Montagu was beheaded on 17 October 1409 in front of a large crowd in Paris, at the Gibbet of Montfaucon. 
His name was rehabilitated several years later, obtained by his son Charles, and his remains were interred in a lavishly built tomb at the Monastery of the Celestines of Marcoussis, which Jean de Montagu had greatly expanded between 1402 and 1408.
Children.
Jean married Jacqueline de La Grange, c. 1380, daughter of Étienne de La Grange, President of the Parliament of Paris, and Marie Dubois. They had: 