Catherine, Princess of Wales, is presiding over her annual Yuletide celebration at Westminster Abbey, with a congregation comprising dignitaries, stars, and everyday helpers who have supported their local areas.
The 1,600 guests will hear a selection of traditional hymns, orchestral pieces, and literary excerpts from actors such as Kate Winslet and Chiwetel Ejiofor.
The central message of the event, held in the atmospheric historic church on Friday, is kindness and showing love to others.
In the audience are Jonathan and Anna Cordiner, whose young girl was lost to a brain tumour, and who established a foundation, Kayleigh's Wee Stars, to aid parents with a youngster facing a life-limiting condition.
"The time, care and compassion you give, often discreetly and without words, and without any hope for reward or acknowledgement, make an extraordinary difference to the circumstances of individuals," Her Royal Highness stated in a message before the festive gathering.
The Princess of Wales is continuing her own steady comeback to the public eye after her cancer diagnosis and chemotherapy, in November making her major oration since 2023, in which she reflected on recognising the "selfless, commonly overlooked efforts of carers".
Guests arriving at the Abbey will enjoy performances from young musicians supported by the Future Talent organisation, set up with the help of the late Duchess of Kent to increase availability of music lessons.
Trumpeter Carys Wood, 18, who performs on the trumpet and is from Pembrokeshire, has been helped by the trust, with grants helping towards equipment, teaching, and travel fees - and she said it was "incredible" to be playing at the concert.
"Pursuing music is often costly," Carys said. She is now studying at the Royal Academy of Music, and added that "each individual ought to be given the possibility" to cultivate their performance abilities.
Eliza, Carys's sister who is 11, who performs on the brass instrument, will be present at the Abbey. "I never thought I'd be able to play there in front of so many distinguished guests," she said.
Attending the service will be people from various age groups.
That will include nine-year-old Saphia Turner, honouree of a young hero award, who sells artwork and carries out sponsored challenges to generate funds for community pantries.
The Abbey has been decorated with handcrafted festive wreaths, with well-known chef Mary Berry and flower expert Simon Lycett assisting in their creation.
Taking to the stage will be Katie Melua, the Westminster Abbey choristers and a maritime folk band from Cornwall, the group Fisherman's Friends, who said the chance to take part was "the perfect culmination."
The Together at Christmas carol concert will be aired by ITV1 on Christmas Eve.
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