The Princess of Wales is hosting her yearly Yuletide celebration at the iconic London venue, with a congregation comprising members of the royal family, famous faces, and community champions who have supported their local areas.
The 1,600 guests will enjoy a blend of carols, music and readings from stars like Kate Winslet and Chiwetel Ejiofor.
The central message of the concert, held in the atmospheric historic church on Friday, is kindness and showing love to others.
Attending the event are Anna and Jonathan Cordiner, whose daughter died of a brain tumour, and who founded an organisation, a support fund, to support families who have a child with a terminal illness.
"The dedication, empathy, and kindness you show, often discreetly and without words, and without any expectation or recognition, make an profound impact to the circumstances of individuals," wrote Catherine in a letter ahead of the festive gathering.
The Princess of Wales is continuing her own steady comeback to the public eye following her health challenges and treatment, last month delivering her first public speech for two years, in which she discussed recognising the "quiet, often invisible work of caring".
Those coming to the Abbey will be entertained by budding artists aided by the Future Talent charity, co-founded by 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 supported by the trust, with grants helping towards musical instruments, lessons and travel costs - and she said it was "amazing" to be performing at the evening's event.
"Music can be very expensive," Carys said. She is now studying at the renowned conservatoire, and added that "all people deserve the chance" to cultivate their performance abilities.
Eliza, Carys's sister who is 11, who is a euphonium player, will be present at the Abbey. "It's unbelievable that I get to perform here in front of so many important people," she said.
Attending the service will be people from various age groups.
That will feature Saphia Turner, aged nine, recipient of a prize for youthful altruism, who creates and sells art and completes fundraising tasks to generate funds for local food charities.
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 recording artist Katie Melua, the Abbey's own choir and a nautical singing ensemble, the Fisherman's Friends, who said the opportunity to perform was "a dream come true."
This annual carol service will be aired by ITV1 on Christmas Eve.
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