Her Royal Highness has organised her annual festive musical service at the historic Abbey, with a congregation comprising dignitaries, stars, and everyday helpers who have supported their local areas.
The sizable congregation will hear a blend of traditional hymns, orchestral pieces, and literary excerpts from stars like Kate Winslet and Chiwetel Ejiofor.
The focus of the service, held in the glowing Westminster Abbey on Friday afternoon, is kindness and showing love to others.
In the audience are a couple named the Cordiners, whose young girl was lost to a brain cancer, and who established a foundation, Kayleigh's Wee Stars, to help households where there is a terminally ill child.
"The time, care and compassion you give, often quietly and unspoken, and without any thought of thanks or praise, make an remarkable change to the lives of others," wrote Catherine in a message before the concert.
The princess has been making her own steady comeback to public life following her health challenges and treatment, recently giving her first public speech for two years, in which she reflected on recognising the "quiet, often invisible work of caring".
Those coming to the Abbey will enjoy performances from young musicians supported by the Future Talent charity, established in part by the former royal to widen access to musical tuition.
Trumpeter Carys Wood, 18, who is a trumpet player and is from Pembrokeshire, has been supported by the organisation, with funding assisting with instruments, tuition, and transportation expenses - and she said it was "incredible" to be performing at tonight's service.
"Musical pursuits are frequently pricey," Carys said. She is now a student at the renowned conservatoire, and added that "all people deserve the chance" to hone their artistic talents.
Carys's 11-year-old sister, Eliza, who is a euphonium player, will be present at the Abbey. "I never imagined I would perform in front of so many distinguished guests," she said.
Attending the service will be representatives of different generations.
That will include young Saphia Turner, nine, honouree of a youth community award, who creates and sells art and completes fundraising tasks to raise money for community pantries.
The Abbey has been festooned with custom-created holiday decorations, with well-known chef Mary Berry and flower expert Simon Lycett helping to make them.
Among the musical performers will be recording artist Katie Melua, the Abbey's own choir and a Cornish sea shanty group, the group Fisherman's Friends, who said the invitation to sing 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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