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In page Isabel de Clare, 4th Countess of Pembroke:

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Although her daughters had many children, Isabel's five sons, curiously, died childless, apart from Gilbert, who before he inherited the earldom had an illegitimate daughter he married off to a son of the Welsh lord Maelgwyn Fychan in 1240.[5] This failure in heirs is supposedly attributed to a curse placed upon the Marshal family by the Irish Bishop of Ferns, Albin O'Molloy.[6] The title of marshal subsequently passed to Hugh de Bigod, husband of Isabel's eldest daughter Maud, while the title of Earl of Pembroke went to William de Valence, 1st Earl of Pembroke, the husband of Joan de Munchensi, daughter of Joan Marshal. He was the first of the de Valence line of the earls of Pembroke.[citation needed]