Someone here has mentioned what I think, i.e. that Harry has 'the look' of his maternal grandfather and Spencer cousins in his facial mix. And yes, I saw the late Earl Spencer in the flesh, just as I have seen all of the royal family.
Another reason why I believe Harry to be Charles' son is that my mother has, on tapes, many videos of the Queen with her family, both on public occasions and more private moments. Time and again, the Queen is walking holding Harry's hand; bending to smile and laugh with him; ruffling his hair, i.e. displaying all of the usual sort of affection that a grandparent shows a small child. I do not believe that she would ever have behaved in this way if she had the slightest doubt that Harry wasn't her natural grandson. Given her well known antipathy towards Diana, I can not imagine that she would show Diana's son any obvious affection if were not Charles' son, as well.
Someone also intimates that Hewitt's fellow officers might know 'something', and that I don't believe either. If Hewitt told them that he was Harry's father, we'd know about it by now. We can no longer assume that officers are gentlemen - look at Hewitt's unconscionable behaviour.
These sorts of rumours are often attached to royalty, including Her Majesty. In the past, I've read that Lord Carnavon is Andrew's father (Andrew looks like Carnavon and is built like him and Carnavon's sons) and that Lord Plunket is Edward's father (they certainly share remarkable physical similarities). Where does all of this stop?
Whereas I liked Diana, I didn't think her particularly intelligent. Even so, I strongly doubt that when having an affair with another man that she wouldn't have known about and used contraception. To insinuate, further, that she might deliberately have imposed a bastard child on the royal family out of revenge alone, is to claim that she was an evil, vindictive, sociopath, and I don't believe that, either.