A lot is known for certain of the ancestry of the Godwins, the family of the last Anglo-Saxon King of England, Harold II. When King Edward the Confessor died in January 1066 his closest relative was his great-nephew, Edgar the Ætheling, but he was young and lacked powerful supporters. Harold was the head of the most powerful family in England and Edward's brother-in-law, and he became king. In September 1066 Harold defeated and killed King Harald Hardrada of Norway at the Battle of Stamford Bridge, and Harold was himself defeated and killed the following month by William the Conqueror at the Battle of Hastings.
The theoretical Cerdicinga ancestry of the Godwinsons is not as cut and dried as this piece of work presents it. Apparently my copy of Frank Barlows book was printed without his dismissal. In my (ca. 46) years studying this question, I've learned that historians, by-and-large, make lousy genealogists; (probably because many of them think so little of genealogical matters). It is, therefore, not the wisest of moves to reject the work(s) of genealogists, on the biased nay-saying of historians. I have an MA in Medieval European history, and have had material on this topic published.