You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
I don't think this has been done before? What if Robert Curthose, William the Conqueror's oldest son, defeats King Henry I at the Battle of Tinchebrai. Can he claim the English throne? Will he be able to hold his duchy? What if Henry I was killed? What of Robert's children?