Hours after the final part of the Duke and Duchess of Sussex's documentary series dropped on Netflix, the royal family presented a united front at the event.
Smiling and looking relaxed, the Princess of Wales arrived before 4.20pm dressed in an elegant, deep-red coat dress with matching shoes and clutch bag.
She greeted clergy at the door of the abbey before going inside where she chatted with guests and enthusiastically high-fived some children.
The princess met and thanked those taking part in the service, including actor Hugh Bonneville and singer Melanie C.
Laughing and joking with the guests, the Princess of Wales was heard telling singer Alfie Boe about her own musical skills, saying she needed more practice singing.
“On the piano, you can slightly hide away a bit more than you can do singing,” she said.
“Actually my children probably wouldn’t forgive me — I’m not sure whether they think I’ve got a particularly good singing voice. I’ll have to have some lessons.”
She chatted with Melanie C, boxer Nicola Adams, singer Craig David and musician Alexis French.
Kate said she knows how busy this time of year is for everyone as she told them she was “hugely grateful” for their participation.
She also chatted with Princesses Eugenie and Beatrice before coming back out to welcome her husband and two children, who arrived before 5pm.
Royal children at the jubilee — in pictures
More than 1,800 people are gathering in the abbey for the concert, staged to recognise the “selfless efforts of individuals, families and communities across the UK, and celebrate and showcase the joy that human connection and togetherness can bring”.
Kensington Palace said the second carol service the Princess of Wales has held is dedicated to the late Queen Elizabeth II and the values she demonstrated throughout her life, including “duty, empathy, faith, service, kindness, compassion and support for others”.
The palace said these principles are “shared and personified by the inspirational guests who have been invited to the abbey in recognition of their tireless work to help and care for those around them”.
Prince William and Catherine, Duchess of Cambridge with their children — in pictures
A Christmas tree in the abbey was decorated with small Paddington Bear decorations, a nod to the late queen’s famous sketch, while guests were greeted with atmospheric snowflakes from a snow machine as they arrived at the entrance.
The palace tweeted pictures of the decorations and said: “Getting ready to welcome our #TogetherAtChristmas guests, celebrating those who have gone above and beyond in their communities and paying tribute to Her Late Majesty The Queen.”