The shocking announcement came after weeks of wild speculation and conspiracy theories about her well-being and whereabouts.
Now Ms Smith said that she hoped Kate’s brave move would dismiss any further conspiracy theories and allow her to recover.
She said: “I think they’ll have to leave her alone. The palace will make sure they leave her alone.
“It would be ghoulish if they followed her to treatment. I hope they will show common decency, which maybe they don’t have in great supply.
“I hope they will stop speculating on all sorts of dire and ludicrous things.”
The royal author claimed her palace sources have been “trying to come to grips to manage this maelstrom of opinions and speculation and vicious theories” and are now “in a state of shock”.
She added that speculation on social media is “much, much harder to control.”
Meanwhile, the Prince and Princess of Wales are said to be “extremely moved” by the public’s warmth and support as tributes continued to pour today from around the world.
People have flocked to the royals’ main London residence, Kensington Palace, as well as to Windsor Castle, where they spend most of their time, to show support for the princess, with many leaving flowers.
A Kensington Palace spokesperson said: “The prince and princess are both enormously touched by the kind messages from people here in the U.K., across the Commonwealth and around the world in response to Her Royal Highness’ message.
“They are extremely moved by the public’s warmth and support and are grateful for the understanding of their request for privacy at this time.”
