Claim: Empress Matilda was the daughter of the king of England.

Robert FitzRoy , 1st Earl of Gloucester -LRB- before 1100 -- 31 October 1147 -RRB- -LRB- alias Robert Rufus , Robert de Caen , Robert Consul -RRB- was an illegitimate son of King Henry I of England . He was the half-brother of the Empress Matilda , and her chief military supporter during the civil war known as The Anarchy , in which she vied with Stephen of Blois for the throne of England .