Prince Harry and Meghan Markle are shown their place and future in the royal family at the annual Commonwealth Day service at Westminster Abbey in 2020.
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He added that this happened after "Palace officials decided to publicly humiliate [Harry and Meghan]".
The royal writer wrote: "Two days later, on March 9, the reality came to the fore. Harry was told he and Meghan could not attend the family procession through Westminster Abbey for the annual Commonwealth Day service, after a monumental An argument broke out.
“Although Harry and Meghan were listed to follow the Queen in the order of service, Palace officials have revised their decision. Sussexes suspicious of the Sussexes decided to publicly humiliate them.
"Harry was told that after stepping down from royal duties, he and Meghan would sit and wait with the congregation. The prospect of a televised image of their separation at the Abbey shocked him".
He continued: "By then they were well aware of Kate and William's animosity. William had not welcomed the brother and Kate was far from her sister-in-law.
"Ultimately, to put an end to the controversy, William and Kate agreed that they would also wait with Harry and Meghan. As members of the royal family entered the abbey, the broken relationship could not be hidden.
"Kate had evacuated to the Sussexes and William's greeting was cold. Harry looked tense. There was a look of joy on Meghan's face."