There are more than 60 mentions of Camilla in Spare, with Harry also taking aim at his father and older brother Prince William in the book.
Princess Diana’s former butler Paul Burrell advised Harry and his wife Meghan Markle to “live a long and happy life” in America and not attend the ceremony in May.
He told Closer Magazine: “The King’s wrath is yet to come down on his son. He has criticised the woman he loves in public.
“Harry and Meghan should stay in America and live a long and happy life there. There’s not a life for them here now. They’ve turned their back on the Royal Family, the country and the people of the country.”
Mr Burrell, who was Princess Diana’s butler for 10 years until her death in 1997, added that it would be difficult for Harry to see Camilla “where his mother could have been”.
The date also falls on the same day as their son Prince Archie’s fourth birthday, another possible reason for Meghan to remain home.
If the family do make the trip back to the UK it is unlikely Archie and his younger sister Princess Lilibet will be at the Coronation as they are still so young.
This comes as Harry and Meghan were no-shows at the 2023 Oscars last Sunday, with a PR expert claiming they did so to avoid negative press.
Carla Speight, PR consultant, said: “Their documentary wasn’t nominated. Meghan’s not currently acting and I don’t think Harry has any plans to either, though stranger things have happened with them recently.
“If they showed up to the Oscars, it would raise many questions as to why and ultimately it wouldn’t be a good look for them as it makes no sense.”
She told the Express there were only three possible reasons for them to attend the prestigious ceremony, and none of those were applicable this year.
She added: “Either they’ve been nominated, are networking or have a project they want to plug. Harry and Meghan don’t have any of those reasons to be there, so it’s no surprise they weren’t there.”