Her Royal Highness has organised her annual Yuletide celebration at the historic Abbey, with attendees featuring royals, celebrities and local heroes who have supported their local areas.
The large audience will hear a selection of carols, music and readings from performers including Chiwetel Ejiofor and Kate Winslet.
The theme of the concert, held in the candle-lit Abbey on Friday, is generosity and expressing affection towards one's neighbour.
Attending the event are Anna and Jonathan Cordiner, whose young girl was lost to a brain cancer, and who established a foundation, Kayleigh's Wee Stars, to support families who have a child with a terminal illness.
"Your efforts, love, and understanding, often quietly and unspoken, and without any expectation or recognition, make an remarkable change to the lives of others," the Princess expressed in a letter ahead of the carol service.
The princess has been making her own measured re-emergence to public life after her cancer diagnosis and chemotherapy, last month delivering her first public speech for two years, in which she talked about recognising the "selfless, commonly overlooked efforts of carers".
Those coming to the Abbey will be entertained by young musicians aided by the charitable trust Future Talent, set up with the help of the Duchess of Kent to broaden opportunities for instrumental training.
Carys Wood, aged 18, who plays the trumpet and is from southwest Wales, has been assisted by the trust, with funding assisting with musical instruments, lessons and travel costs - and she said it was "incredible" to be playing at tonight's service.
"Pursuing music is often costly," the musician remarked. She is now enrolled at the prestigious music academy, 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 also be at the Abbey. "I never imagined I would perform in front of so many notable figures," she said.
Within the audience will be representatives of different generations.
That will encompass Saphia Turner, aged nine, winner of a young hero award, who sells artwork and carries out sponsored challenges to collect donations 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 singer Katie Melua, the Abbey's own choir and a maritime folk band from Cornwall, the group Fisherman's Friends, who said the opportunity to perform was "the perfect culmination."
The festive event titled 'Together at Christmas' will be aired by television on December 24th.
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