Well, it depends on who's story you believe. It is pretty certain that Edward promised the throne to William in 1051, it is also true that Edward hated the Godwins with a passion, it is also true that Harolds claim to the throne was to say the least, tenuos, inthat his only claim was the Edward was married to his sister and it looks very much like the marriage was never consummated anyway. So, there are some people who consider that Harold was in fact a usurper, and William was the rightful king.