George Burton Adams,
The History of England from the Norman Conquest to the Death of John…
“ Robert of Caen, so called from the place of his birth, was created Earl of Gloucester, and was married to Mabel, heiress of the large possessions of Robert Fitz Hamon in Gloucester, Wales, and Normandy. Robert of Gloucester, as he came to be known, was the eldest of Henry's illegitimate sons, born before his father's accession to the throne, and he was now in the vigour of young manhood. ”
