[a] To prevent further hostilities during his invasion of England, William I married his daughter Constance to the new duke Alan in 1087.

William of Malmesbury wrote that Constance was unpopular at the Breton court because of her "severe and conservative" manner.

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.

In 1098 Alan went on the First Crusade,[5] as part of the army of Robert Curthose, leaving Ermengarde as his regent, and returned in 1101.

He had two illegitimate sons: Alan IV died in 1119 at the monastery of Redon, where he had retired after his abdication in 1112, and separation from his wife Ermengarde.