Sources

1) Source: The Ecclesiastical History of England and Normandy: Volume III "Roger de Beaumont, a wise and discreet nobleman... That house was founded by his father, Humphrey de Vieilles... There Robert de Beaumont, son of Humphrey, Who was slain by Roger de Clare, was buried, and Roger himself, his brother... made a good end in that monastery, some years after his profession as a monk. He left his sons, Robert and Henry, the appointed heirs of his domains... Robert became earl of Mellent in the Vexin, as heir to Hugh, his mother Adeline's brother, and in England fortunately received from King Henry a grant of the earldom of Leicester... His brother Henry earned the earldom of Warwick by his valour and loyalty, and obtained for wife the beautiful Margaret, daughter of Geoftrey, earl of Morton... She bore her husband two sons, Roger, and Robert de Neubourg who became illustrious in England and Normandy during the reign of King Henry" (Data from secondary evidence)
2) Source: English Baronies: a Study of Their Origin and Descent, 1086-1327. Reference: Pages 93-94: Warwick (Questionable reliability of evidence)
3) Source: The Ecclesiastical History of England and Normandy: Volume III "Robert, earl of Mellent, expired on the nones [the 5th] of June" (Data from secondary evidence)