It can't possibly turn out be the same book which was planned a year ago. I can see how an upbeat version was possible back then, but circumstances have changed dramatically and no credible biography can ignore what's happened in the last six months.
It probably didn't start out intending to be a dirty laundry version, but it may well turn into one, and I would envisage that's got a lot to do with William's apparent simmering rage. He must feel betrayed.
One day in the not so distant future, William will be in charge of the royal purse strings and I suspect he'll be less malleable than his father. H might do well to keep that in mind.