Just to play the devil's advocate.
Let's say Harry, Charles and Hewitt take the DNA test "to put the matter to rest" and satisfy our curiosity. And the result shows definitively that Hewitt is Harry's father. Should Harry be stripped of his HRH and his lifestyle (and all the money he inherited from the Queen Mother) and then be known as Harry Hewitt or Harry Spencer?
FYI, I think Harry is Prince Charles' son, although he, like William, has the good fortune to resemble the more photogenic of their parents, and I wish people would let this subject go. It causes more trouble than it is worth, and it probably bothers Harry quite a lot.