Lady Sarah Chatto showed solidarity with the Prince and Princess of Wales as they joined other members of the royal family at the special Christmas concert on Thursday evening.
The Queen's niece was seen arriving at Westminster Abbey, where she joined the likes of her cousin King Charles and his wife Queen Consort Camilla as well as the Countess of Wessex.
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Lady Sarah, who arrived at the abbey with her husband Daniel Chatto, was dressed in an elegant dark blue coat dress with a matching clutch bag and diamond-encrusted earrings.
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Other members of the royal family who were at the concert included Princess Beatrice and her husband Edoardo Mapelli Mozzi, Princess Eugenie and Jack Brooksbank, and Zara Tindall and her husband Mike.
The family reunion came hours after the final part of Prince Harry and Meghan Markle's tell-all documentary dropped on Netflix.
In the final part of the series, Harry called the bullying allegations against Meghan, which appeared shortly before their Oprah Winfrey interview, "institutional gaslighting", comparing her treatment to that of his late mother Diana, Princess of Wales. Both Buckingham Palace and Kensington Palace declined to comment on the documentary.
Lady Sarah Chatto pictured on Thursday evening
Princess Kate's second carol service was dedicated to the late Queen and the values she demonstrated throughout her life, including "duty, empathy, faith, service, kindness, compassion and support for others".
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Kensington 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".
The Princess of Wales also had the support of her parents Carole and Michael Middleton, her sister Pippa and her husband James Matthews, and her brother James and his wife Alizee.