Margaret de Mortimer, d. 5 May 1337, daughter of Sir Roger de Mortimer, Earl of March and Joan de Geneville. [Magna Charta Sureties]
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He [Thomas de Berkeley] m. 1stly, in or shortly bef. 25 July 1320 (Papal disp. to remain married with legitimisation of past issue dated Sep 1329), Margaret, daughter of Roger Mortimer, Earl of March, by Joan, de jure suo jure (according to modern doctrine) Baroness Geneville, daughter and heir of Sir Piers de Geneville (2nd but 1st surviving son and heir apparent of Geoffrey, 1st Lord Geneville). She d. 5 May 1337, being under 30, and was buried at St. Augustine's, Bristol. [Complete Peerage II:129-30, XIV:87]