How the Royals celebrate Christmas at Sandringham

But the American former actress is in the rare position of already having spent December 25 with the Windsors.

She became the first non-married partner invited to Christmas lunch at Sandringham with the Queen in 2017.

Now an HRH and a duchess, the ex-Suits star is seven months into her royal life, and due to give birth to a royal baby in the spring.

The traditions followed by the royal family at Christmas are a little different from many households in the UK.

While most people across the country open their presents on Christmas Day, the royal family still keep to the German practice of opening their gifts on Christmas Eve.

Known as Heiligabend Bescherung (which translates as Christmas Eve exchanging presents), the tradition was popularised by Queen Victoria and Prince Albert.

The Queen, the Duke of Edinburgh and other royals usually congregate in the White Drawing Room at Sandringham House the day before Christmas to put the finishing touches to a 20ft (6m) tree cut from the estate.

Presents are placed on a white linen-covered trestle table, with cards marking exactly where the piles of gifts should be put.

The Queen likes practical presents, but not overly extravagant ones, and the royals also reportedly like to exchange joke or non-costly quirky gifts.

Kate revealed that she was left stumped over what to buy the monarch for Christmas during her first stay at Sandringham.

"I thought back to what would I give my own grandparents. And I thought 'I'll make her something.' Which could have gone horribly wrong," the duchess said.

"But I decided to make my granny's recipe of chutney. I was slightly worried about it, but I noticed the next day that it was on the table."

Diana, Princess of Wales, once fell foul of the royal rules on present-giving, apparently buying cashmere sweaters as her first festive royal presents, and getting joke gifts such as a loo-roll holder in return.

Afterwards, they dress for dinner, with the men in black tie and the women in evening gowns, with the table set with the finest china.

Sarah, Duchess of York, once described the royal Christmas as "exhausting", having changed outfits seven times in 24 hours.

Sometime after 10pm, on a signal from the Queen, the corgis are led out and the ladies adjourn, leaving the Duke of Edinburgh to serve port or brandy to the men.

On Christmas Day, the royals awake to find stockings filled with small gifts and fruit at the foot of their beds.

Their walk to the morning service at the Church of St Mary Magdalene on the royal estate is a traditional event where they greet well-wishers.

Back at the house, lunch is prepared by their staff and served at 1pm, and the royals indulge in a giant turkey, reared at Sandringham.

The Queen sometimes quietly leaves the room and lets her family watch the national address by themselves, as she views it alone to see how it comes across.

Boxing Day, when the royals enjoy a breakfast buffet of kedgeree, bacon and eggs, often involves outdoor pursuits such as shooting, riding and walking.