Margaret Fiennes, Baroness Mortimer

Margaret de Fiennes, Baroness Mortimer (after 1269 – 7 February 1333), was an English noblewoman born to William II de Fiennes, Baron Tingry and Blanche de Brienne. Her paternal grandparents were Enguerrand II de Fiennes and Isabelle de Conde. Her maternal grandparents were Jean de Brienne and Jeanne, Dame de Chateaudun.
Margaret had a sister, Joan de Fiennes (c. 1273 - before 26 October 1309), whose daughter, Margaret Wake, was the mother of Joan of Kent. Therefore, Margaret de Fiennes was a great-aunt of Joan, the Fair Maid of Kent. Margaret de Fiennes was also a first cousin of Humphrey de Bohun, 4th Earl of Hereford.
In September 1285, when she was fourteen or fifteen years old, Margaret married Edmund Mortimer of Wigmore, 2nd Baron Mortimer, the son of Roger Mortimer, 1st Baron Mortimer and Maud de Braose. They had eight children.

• Roger Mortimer, 1st Earl of March (25 April 1287 – 29 November 1330) married Joan de Geneville, by whom he had twelve children. Through this union are descended the last Plantagenet monarchs of England from King Edward IV to Richard III, and every monarch of England after King Henry VII.
• Maud Mortimer, married Sir Theobald II de Verdun, by whom she had four daughters, Joan, Elizabeth, Margaret, and Katherine de Verdun. Queen consort Catherine Parr is a descendant of Margaret de Verdun by her marriage to Sir Thomas de Crophull.
• John Mortimer, accidentally slain in battle by John de Leyburne.
• Walter Mortimer, a priest, Rector of Kingston.
• Edmund, a priest, Rector of Hodnet and Treasurer of the cathedral at York.
• Hugh Mortimer, a priest, Rector of the church at Old Radnor.

They also had two daughters who became nuns; Elizabeth and Joan.