Fulk then married his daughter Sibylla to William Clito , heir to Henry 's older brother Robert Curthose .
Henry had the marriage annulled to avoid strengthening William 's rival claim to Henry 's lands .
Fulk then married his daughter Sibylla to William Clito , heir to Henry 's older brother Robert Curthose , but Henry had the marriage annulled to avoid strengthening William 's rival claim to his lands .