The former king is desperate to clean up his bad press, that he is solely responsible for, because he probably feels the end is coming soon as his age and conditions catch up with his health.
As a Spaniard abroad since the 1980s, I stopped caring for him after the trip to Botswana set up by his mistress to kill poor elephants for photo ops next to their lifeless bodies. I'm glad he rescued us from Franco and its supporters twice, but as the father figure of our nation I would have preferred his well-known scandals had stopped decades ago. He became arrogant and almost destroyed everything he built, and Felipe inherited this mess.
That book will probably be excuses and more excuses with absolutely no acknowledgement of his behavior, or the children born out of other women, his infidelities toward the queen, his money schemes. Etc.
There's no digital ink that can cover that up.