Her Royal Highness has organised her yearly Yuletide celebration at the historic Abbey, with attendees featuring members of the royal family, famous faces, and community champions who have supported their local areas.
The 1,600 guests will enjoy a selection of carols, music and readings from actors such as award-winning actors.
The central message of the concert, held in the atmospheric historic church on Friday, is compassion and demonstrating care for others.
Attending the event are a couple named the Cordiners, whose child passed away from a brain tumour, and who founded an organisation, Kayleigh's Wee Stars, to aid parents with a terminally ill child.
"The dedication, empathy, and kindness you show, often without fanfare or recognition, and without any hope for reward or acknowledgement, make an remarkable change to the well-being of people," wrote Catherine in a note prior to the carol service.
The royal has been undertaking her own steady comeback to public life after her cancer diagnosis and chemotherapy, recently giving her first public speech for two years, in which she talked about recognising the "selfless, commonly overlooked efforts of carers".
Guests arriving at the Abbey can listen to talented youth performers aided by the Future Talent organisation, set up with the help of the late Duchess of Kent to widen access to instrumental training.
An 18-year-old named Carys Wood, who is a trumpet player and is from southwest Wales, has been helped by the charity, with awards contributing to equipment, teaching, and travel fees - and she said it was "awesome" to be performing at the evening's event.
"Music can be very expensive," she stated. She is now a student at the renowned conservatoire, and added that "everyone should have the opportunity" to cultivate their performance abilities.
Eliza, Carys's sister who is 11, who performs on the brass instrument, will also be at the Abbey. "It's unbelievable that I get to perform here in front of so many notable figures," she said.
Within the audience will be representatives of different generations.
That will encompass Saphia Turner, aged nine, recipient of a young hero award, who sells artwork and carries out sponsored challenges to collect donations for community pantries.
The Abbey has been festooned with handcrafted festive wreaths, with TV cook Mary Berry and florist Simon Lycett contributing to their design.
The musical lineup includes singer Katie Melua, choristers from Westminster Abbey and a maritime folk band from Cornwall, the group Fisherman's Friends, who said the opportunity to perform was "a dream come true."
The Together at Christmas carol concert will be broadcast on a major network on Christmas Eve.
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