Her Royal Highness has organised her customary Yuletide celebration at the iconic London venue, with a congregation comprising royals, celebrities and local heroes who have supported their local areas.
The 1,600 guests will listen to a blend of traditional hymns, orchestral pieces, and literary excerpts from performers including award-winning actors.
The theme of the service, held in the candle-lit Abbey on Friday, is compassion and demonstrating care for others.
In the audience are Anna and Jonathan Cordiner, whose daughter died of 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 discreetly and without words, 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 concert.
The royal has been undertaking her own gradual return to official duties after her cancer diagnosis and chemotherapy, last month delivering her major oration since 2023, in which she reflected on recognising the "selfless, commonly overlooked efforts of carers".
Guests arriving at the Abbey will be entertained by young musicians aided by the Future Talent organisation, set up with the help of the late Duchess of Kent to increase availability of instrumental training.
Trumpeter Carys Wood, 18, who is a trumpet player and is from Wales, has been assisted by the charity, with funding assisting with instruments, tuition, and transportation expenses - and she said it was "incredible" to be playing at the evening's event.
"Musical pursuits are frequently pricey," she stated. She is now enrolled at the Royal Academy of Music, and added that "all people deserve the chance" to develop their musical skills.
Her younger sibling Eliza, aged 11, who plays the euphonium, will be present at the Abbey. "It's unbelievable that I get to perform here in front of so many important people," she said.
Within the audience will be representatives of different generations.
That will feature young Saphia Turner, nine, winner of a prize for youthful altruism, who produces drawings and undertakes charity feats to raise money for community pantries.
The Abbey has been festooned with custom-created holiday decorations, with TV cook Mary Berry and florist Simon Lycett helping to make them.
The musical lineup includes recording artist Katie Melua, the Abbey's own choir and a Cornish sea shanty group, the Fisherman's Friends, who said the opportunity to perform was "the icing on the cake for us."
The Together at Christmas carol concert will be broadcast on ITV1 on Christmas Eve.
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