William of Malmesbury also alleged that Alan IV had Constance poisoned to death, but this was unverified However, Orderic Vitalis wrote that as duchess, Constance did all she could to further the welfare of the Bretons, who grieved deeply at her death in 1090.
William dari Malmesbury juga menyatakan bahwa Alain IV meracuni Constance, namun hal tersebut belum terbukti kebenarannya Akan tetapi, Ordericus Vitalis menulis bahwa Constance berusaha semaksimal mungkin untuk memajukan kesejahteraan Breton, yang sangat berkabung atas kematiannya pada tahun 1090.