William of Jumièges, the monk who chronicled the 1066 Norman conquest of England, names Constance second among the daughters of King William and Queen Matilda.

[2] In 1086, Constance's father arranged a marriage between the duke of Brittany Alan Fergant and Constance, who was already nearly 30, to ensure peace at his Western border.

William of Malmesbury, an early 12th century historian, wrote that her "severe and conservative manner" made Constance an unpopular duchess.

According to his contemporary, Orderic Vitalis, however, Constance was caring, considerate, and well-liked by her subjects.

William of Malmesbury alleges that her husband had their servants poison her.