Isabel daughter of William (born c. 1165) (Gaelic: Isibéal nighean Uilleim) 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 (died 1227).
They had the following children: