The Duchess, who is around six months pregnant, hosted her parents Carole and Michael and siblings Pippa Middleton and James Middleton for Christmas lunch for the first time ever. They have been staying at the Cambridges' new country home Anmer Hall since last Thursday.
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It's a sign of how attentive and sensitive William is towards his wife that he asked permission from the Queen for the couple to spend the big day with her family.
A source said the pregnant royal was looking forward to organising the kind of perfect family Christmases she remembered from her childhood.
Pippa Middleton has previously written about playing board games, going for hearty walks and dad Michael entertaining everyone by dressing up in silly costumes.
This year the Cambridges attended the formal Christmas Eve dinner at his grandmother's Sandringham estate – a compromise that seemed to suit the Queen as she was beaming away at church the next day.
Along with the Middletons, William and Kate also attended the traditional Christmas morning service at St Mary Magdalene Church on the estate.
Sadly for well-wishers Prince George had been left behind with his nanny because as his mother explained: "You would have heard him in the church".
One royal fan Kim Dawson asked William how the 17-month-old toddler was.
She said: "He said Prince George was really, really well and said that they've left him at the nursery because it's a little bit cold, but they were looking forward to going back to see what destruction he'd caused.
"He wished us a happy Christmas and asked if we were warm enough and he said he was very grateful for all the flowers."
The Duchess was impeccably turned out as always in a tweed coat and Lock & Co hat as she collected flowers and tokens from the crowd – but told one onlooker that she "felt big".
Mary Young said: "I told her she looked beautiful but she said she feels big. She doesn't look it".
The royals were led to church by doughty 93-year-old Prince Philip who arrived on foot with Princess Anne and her husband Vice Admiral Sir Timothy Laurence. They were followed by Prince Charles, who was without his wife the Duchess of Cornwall. She couldn't attend because of a bad back.
Also at the service were the Duke of York with his elegantly turned out daughters, Princess Eugenie and Princess Beatrice. The family group was completed by Princess Anne's son Peter Phillips and his wife Autumn.