I have never, ever been able to see the slightest resemblance between Harry and Charles. Nothing. That doesn't mean they're not related though.
Mind you, I fail to see what a resemblance between Harry and his cousin (George McCorquodale) has to do with anything? They're related through his mother, so his father would be irrelevant.
And whilst we shouldn't speak ill of the date and I respect William and Harry's clear affection for their late mother, I think she was a complete fruit-cake and all those who were weeping and wailing as if they'd lost a close relative, had no idea of who she was or what she was really like.