Charles, William, Camilla and Kate will however be there and have been dubbed the "new Fab Four" as they take on the Queen’s duties after she announced last week that she was too ill to attend.

       Meghan and Harry are outspoken on the issue of climate change, but their work risks being overshadowed by the global summit.

       During an interview with Oprah in May, Harry said: “I believe even more that climate change and mental health are two of the most pressing issues that we’re facing.”

       It comes as Meghan and Harry have been said to have "isolated" themselves from the Royal Family after they chose to leave the Firm last year to focus on Meghan’s mental health.

       Royal author Tom Bower said: “Harry and Meghan have totally isolated themselves. They seem to think they will be stronger by cutting people out, but they’re really just alienating their families.

       “I believe Meghan is a very stubborn person, but I think eventually even she’ll realise that this isolated world she and Harry have built for themselves was a poisonous choice.”

       Representatives for the Duke and Duchess of Sussex have been contacted for comment.

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