Isabel daughter of William the Lion
Isabel daughter of William was the illegitimate daughter of William I of Scotland by a daughter of Robert Avenel. She married Robert III de Brus in 1183; they had no children. After his death in 1191, Isabella was married to Robert de Ros, Baron Ros of Wark. They had the following children:
- Sir William de Ros.
- Sir Robert de Ros, was Chief Justice of the Kings Bench. He married Christian Bertram.
- Sir Alexander de Ros, who fathered one child, William, with an unknown wife.
- Peter de Ros.