Camilla, Duchess of Cornwall is unable to head down from Scotland, where she and Prince Charles are currently staying, because she has a day of duties.
The royal, 71, is set to attend a harvest festival, visit a school and step out for another engagement close to the home she and Charles, 69, share in the Highlands, PEOPLE understands.
Her diary was already set when the wedding date was set: “These are long-standing invitations,” says a source at the couple’s Clarence House office.
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Around 800 people are expected in St. George’s Chapel, including most of the senior members of the royal family. Prince Harry and Meghan Markle, who became the Duke and Duchess of Sussex on their wedding day in May, are expected before they head out to Australia, Tonga, Fiji and New Zealand for their much-anticipated tour.
Eugenie’s sister Princess Beatrice, 30, is acting as the maid of honor at Friday’s service.
It was confirmed that Andrea Bocelli will sing at the ceremony, which started at 6 a.m. Eastern Standard Time, and the couple have chosen a red velvet and chocolate cake for their reception.