The Prince of Wales and the Duchess of Cornwall stepped out to attend a morning church service in Windsor with the Earl and Countess of Wessex, and the Duke and Duchess of Gloucester.
The Queen, 95, was absent from the service at St George's Chapel but her annual Christmas speech will be broadcast on TV at 3pm.
It is understood the monarch's absence from the service is a personal choice and follows a precautionary approach seen over the last six months.
The Queen has been joined by Prince Charles and Camilla at her Berkshire abode this year, as she marks her first Christmas without her husband, the Duke of Edinburgh, who passed away in April.
Her Majesty is spending Christmas at Windsor Castle for the second year running after cancelling her annual family gathering at Sandringham amid rising COVID-19 cases.
Take a look at the best photos from the royals' Christmas Day in Windsor…
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Camilla, dressed in a blue and turquoise chequered jacket and matching hat, wished a "Happy Christmas" to members of the press as the couple walked to the chapel.
The royals were greeted at the entrance by the Dean of Windsor before moving inside for the morning service.
The service, which is ticketed, was attended by residents of the Windsor estate and members of the chapel congregation.
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The Earl and the Countess of Wessex were accompanied by their children, Lady Louise, 18, and James, Viscount Severn, 14.
The Queen's cousin, the Duke of Gloucester and his wife, the Duchess of Gloucester were pictured walking to the morning service.
Sophie looked elegant in a navy coat with striking leopard print accessories for the church service.
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The Duchess of Cornwall accessorised with her trusty Chanel bag and a string of pearls.
Camilla also popped on a brightly coloured face mask before heading into the service, in adherance to the latest government guidelines.