A royal treat! Prince William and Kate Middleton are set for merry and bright celebrations this Christmas with Prince George, 11, Princess Charlotte, 9, and Prince Louis, 6.

The Prince and Princess of Wales, both 42, are gearing up to welcome the festive season with their annual trip to Sandringham, where they will join other members of the royal family, The Post can reveal.

Each year, all members of the Firm are invited to the late queen’s country estate in Norfolk, England, where they celebrate Christmas with a family dinner followed by an afternoon of gift-giving.

“Historically, the king always gets there on Christmas Eve but I think he gets there the day before now,” Grant Harrold, former personal butler to the monarch, exclusively tells The Post.

“They’ll probably go on Christmas Eve, but if they’re already at Amber Hall, they’ll probably be up there before, especially with Kate not doing quite as much at the moment.”

“Last Christmas she was probably aware that something wasn’t quite right, so I imagine it was quite a tough Christmas,” he added.

The former royal staffer said this year’s celebrations will be “more positive, based on what we’ve been told.”

“It will be like any other Christmas, focused on the young family. They’re very family orientated, like the late queen, so that will be their focus,” he shared.

Unsurprisingly, Prince Harry, 40, and his wife, Meghan Markle, 43, have once again been snubbed from the invite list this year — marking the sixth year in a row they’ve spent the festive season apart from Harry’s family.

Instead, the Duke and Duchess of Sussex — along with their children Prince Archie, 5, and Princess Lilibet, 3 — will reportedly celebrate Christmas with Markle’s mom, Doria Ragland.

Harry and the “Suits” alum will make their at-home celebrations “extra special” for their two young children, recent reports suggest.

Still, Harrold believes that the Waleses will reach out to the Sussexes to “wish them a Happy Christmas.”

“I think Harry and Meghan themselves will possibly reach out,” he said. “The thing about Christmas, it is about goodwill to others, letting bygones be bygones, forgetting the past, moving into the new year.”

“So if there’s any point in the year that the families are going to communicate or touch base, it’s going to be over Christmas — there’s something magical about Christmas that gets families back together,” he added.

Meanwhile, Princess Catherine will organize a special carol concert that will air on Christmas Eve.

With a new theme each year, December’s service will focus on the importance of love and empathy, and will reflect on “how much we need each other, especially in the most difficult times of our lives.”

Indeed, the beloved royal was dealt a tough start to the year that saw her undergo abdominal surgery in January, which was closely followed by a cancer diagnosis in March.

Her father-in-law, King Charles III, was also diagnosed with cancer earlier this year.

Middleton, who recently announced she was cancer free after completing chemotherapy, will lead the televised festive event at Westminster Abbey on Dec. 6.

Her involvement in this year’s event was previously thrust into doubt given her health woes.

On the day of the service, London’s Westminster Abbey will be filled with 1,600 people who have provided support to their communities.

It will be Princess Catherine’s fourth time staging the “Together At Christmas” carol service. The annual event is supported by the Royal Foundation.