It's supposed to be her that has edited not him. If you choose to believe the origin of that statement on twitter.
I'm not gonna speculate on exactly what has happened, only the facts that the picture released was photoshopped and we aren't talking touch ups.
In it's published format the picture was fake.
The royal angle is that Kate took it upon herself to edit this photo badly, with some unaddressed aim, that was more than just adjusting colours and that caused AP to withdraw it.
It's plausible, but on the balance of probabilities either isn't true or isn't the entire story. moving elements of the image around (or possible blending of more than one image) as has clearly been done, does not fit with the explanation.
There isn't enough evidence to know the full truth of this, unfortunately, so without a whistleblower then all that we have is further distrust of royal statements. But then my trust is already pretty low anyway.