Her Royal Highness has organised her customary festive musical service at the historic Abbey, with attendees featuring royals, celebrities and local heroes who have supported their local areas.
The sizable congregation will enjoy a selection of festive songs, musical performances, and spoken word pieces from actors such as Chiwetel Ejiofor and Kate Winslet.
The focus of the service, held in the atmospheric historic church on Friday afternoon, is generosity and expressing affection towards one's neighbour.
In the audience are Jonathan and Anna Cordiner, whose young girl was lost to a tumour, and who established a foundation, a support fund, to help households where there is a child with a terminal illness.
"Your efforts, love, and understanding, often quietly and unspoken, and without any hope for reward or acknowledgement, make an extraordinary difference to the circumstances of individuals," the Princess expressed in a letter ahead of the festive gathering.
The Princess of Wales is continuing 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".
Those coming to the Abbey will be entertained by young musicians backed by the Future Talent organisation, established in part by the former royal to widen access to musical tuition.
Trumpeter Carys Wood, 18, who plays the trumpet and is from southwest Wales, has been helped by the charity, with funding assisting with musical instruments, lessons and travel costs - and she said it was "amazing" to be taking part in the concert.
"Music can be very expensive," she stated. She is now enrolled at the Royal Academy of Music, and added that "everyone should have the opportunity" to develop their musical skills.
Eliza, Carys's sister who is 11, who plays the euphonium, will likewise attend the Abbey. "I never imagined I would perform in front of so many notable figures," she said.
Among the guests will be representatives of different generations.
That will encompass Saphia Turner, aged nine, recipient of a prize for youthful altruism, who sells artwork and carries out sponsored challenges to generate funds for community pantries.
The Abbey has been adorned with handcrafted festive wreaths, with well-known chef Mary Berry and flower expert Simon Lycett helping to make them.
Taking to the stage will be Katie Melua, the Westminster Abbey choristers and a maritime folk band from Cornwall, the Fisherman's Friends, who said the opportunity to perform was "the icing on the cake for us."
The festive event titled 'Together at Christmas' will be televised and shown on a major network on Christmas Eve.