Leading the arrivals, the 41-year-old royal was the picture of elegance in white fitted flares with gold button detailing and a simple cream knit. Looking a million dollars, the Princess of Wales flashed a big smile for the cameras She layered up with a smart, longline coat by Chris Kerr.
Kate's chic trousers hailed from Holland Cooper. The 'High Waisted Straight Trousers' in ivory retail for £299 and boast a flattering silhouette that suits all body shapes.
Princess Kate added a pair of pointed-toe beige boots and toted a small white handbag to match. She styled her chocolate-hued tresses in voluminous waves with soft layers framing her face.
The appearance was all the more special since she was joined by her beloved children Prince George, ten, Princess Charlotte, eight, and for the first time, Prince Louis, five, who looked absolutely adorable in coordinating festive outfits.
A glamorous beauty look completed the look, including a shimmering pink lip and dewy, light-reflecting highlighter enhancing her cheekbones.
What is the symbolism of wearing white?
Last year, HELLO! sat down with Colour Psychologist and Design Director Tash Bradley to discuss what a power move it is for royal ladies to wear white.
The shade is synonymous with purity and "clarity of thought" - it's a sign of knowing your own mind and being upfront.
Tash explained: "To wear white, you've got to have a lot of confidence you know. You're not hiding anything – you want to show purity. If someone wears white, they're being, not minimalist, but it's very clean. It's very pure, it's very soft." It's a very brave move to put an all-white outfit on."
What is Princess Kate's festive concert in aid of?
A Kensington Palace spokesperson told HELLO! ahead of the concert: "The Princess has been working hard behind the scenes to make sure this year’s Carol Service will be a moment to thank all those who work so hard to support babies, young children and families in our communities across the UK.
"Since launching her Shaping Us campaign in February she’s been shining a light on just how important the first five years are in a baby’s life.
"This year’s carol service will be a celebration of the golden opportunity that the birth of a new baby brings, and she can’t wait to welcome guests to the Abbey."
The carol service took place to honour all those who work to support babies, young children and families in communities across the UK and celebrates the joy a new baby brings.
Guests included those working in early years, which is of course a key focus of Kate’s work through The Royal Foundation Centre for Early Childhood.
Christmas trees, provided by the King from Windsor Great Park and later donated to the local community, were decked with twinkling lights and paper and felt ornaments including holly leaves and miniature trees.
A Christmas Post Box was placed outside the West Door, for children to send handmade cards to other youngsters who might be struggling.