Fitzhamon married Sibyl, daughter of Roger of Montgomery, 1st Earl of Shrewsbury, and Mabel of Bêlleme, by whom he probably only had one child, Mabel, who inherited his great estates and married Robert of Gloucester.
Fitzhamon married Sibyl (or Sybille), apparently the youngest daughter of Roger of Montgomery, 1st Earl of Shrewsbury, and Mabel of Bêlleme, by whom he is said to have had four daughters. His eldest daughter Mabel inherited his great estates and married Robert of Gloucester.