Pierre was the son of unknown parents. The date and place of his birth have not been found.
His wife was Marguerite de Penthièvre. They were married, but the date and place have not been found. Their only known child was Hervé (?->1193).
Note 1
issu des vicomtes de Poher.
L'existence d'une vicomté du Poher est attestée dans un acte antérieur à 1108 qui mentionne, la fondation, "près du château de Carhaix", d'un prieuré Saint-Nicolas, remis par le vicomte du Poher à l'abbaye de Redon
Note 2