Catherine, Princess of Wales, is presiding over her yearly Christmas carol concert at the iconic London venue, with a congregation comprising dignitaries, stars, and everyday helpers who have supported their local areas.
The large audience will hear a mix of carols, music and readings from performers including Kate Winslet and Chiwetel Ejiofor.
The central message of the concert, held in the glowing Westminster Abbey on Friday, is compassion and demonstrating care for others.
In the audience are Jonathan and Anna Cordiner, whose daughter died of a brain cancer, and who founded an organisation, a support fund, to help households where there is a terminally ill child.
"The time, care and compassion you give, often discreetly and without words, and without any expectation or recognition, make an remarkable change to the lives of others," wrote Catherine in a message before the concert.
The royal has been undertaking her own gradual return to public life following her health challenges and treatment, last month delivering her first public speech for two years, in which she discussed recognising the "discreet, frequently unseen labour of caregivers".
Those coming to the Abbey will enjoy performances from young musicians aided by the charitable trust Future Talent, co-founded by the former royal to widen access to music lessons.
Trumpeter Carys Wood, 18, who performs on the trumpet and is from Wales, has been helped by the charity, with funding assisting with musical instruments, lessons and travel costs - and she said it was "awesome" to be performing at tonight's service.
"Musical pursuits are frequently pricey," she stated. She is now enrolled at the renowned conservatoire, 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 notable figures," she said.
Among the guests will be individuals spanning multiple eras.
That will encompass nine-year-old Saphia Turner, winner of a young hero award, who creates and sells art and completes fundraising tasks to raise money for local food charities.
The Abbey has been adorned with specially made wreaths, with well-known chef Mary Berry and flower expert Simon Lycett helping to make them.
Among the musical performers will be singer Katie Melua, the Abbey's own choir and a nautical singing ensemble, Fisherman's Friends, who said the chance to take part was "a dream come true."
This annual carol service will be broadcast on a major network on Christmas Eve.
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