began putting plans in place for the future of the monarchy soon after his cancer diagnosis.It’s believed that details are being kept “highly secret” from the Duke of Sussex, 39.“Because of [Harry’s] previous documentaries, that might be on the mind of not necessarily the King but the Royal household — the office that runs it,” Grant Harrold, who worked for His Majesty for seven years when he was the Prince of Wales, exclusively told The Post.“Harry is still Counsellor of State and privy to top-secret information because technically he is able to step in for the King, so it doesn’t make sense why he wouldn’t be kept in the loop. If he wasn’t still Counsellor of State then that would be a very different matter.”Little to no surprise, it’s believed that Prince William, the heir to the throne, is “at the heart” of the King’s succession plans.“The King has or definitely had a close relationship with Harry — if this is true, I can’t understand why the King wouldn’t want to share his plans,” Harrold said.“Maybe there’s this feeling not to share following all the documentaries and interviews Harry has done.