Margaret de Bohun

According to Wikipedia: "Humphrey de Bohun (b&d 1305) (buried with Mary or Margaret) Mary or Margaret de Bohun (b&d 1305) (buried with Humphrey) " It has thus been speculated that they may have been twins.

From Medlands: The History of the foundation of Walden abbey records the birth “apud Tinehmue” of “Margareta primogenita” to “Humfridus de Bohun” and his wife “Elizabethæ…regis Angliæ Edwardi…filiæ”[592]. A manuscript which narrates the descents of the founders of Lanthony Abbey names (in order) “Margareta…Humfredus…Johannes…Humfredus decimus…Edwardus et Willielmus…Alianora, Margareta secunda, Eneas, Isabella” as the six sons and four daughters of “Humfredus octavus de Bohun, comes Herefordiæ et Essex, constabularius Angliæ et dominus Breconiæ” and his wife “Elizabetham filiam regis Edwardi filii regis Henrici tertii”, adding that the first Margaret died young[593].