He can't be too closely related to the Windsors because they have notoriously small peters. It was said that Edward VIII was incapable of fathering an heir because his penis could not reach the vagina. They say further he may have abdicated for this reason and Elizabeth's father beame king. I've never heard anything about ERII's boys other than they are all average. If William and Harry have any size to them, I'm sure they can thank their mother for yet another extraordinary gift.
Regarding the Spanish prince, he doesn't seem to be having to tough a time at life...