Lady Pamela Hicks will be laid to rest this Saturday at Brightwell Baldwin Church in Oxfordshire, near her home, following her death on June 5 at the age of 97.
The service, scheduled for 3pm, coincides with the King's Birthday Parade at Horse Guards Parade, creating a scheduling dilemma for the monarch.
Whether the King will attend his cousin's funeral remains unclear, though the timing could theoretically allow for both engagements, with the traditional Buckingham Palace balcony appearance typically occurring around 1pm.
The King demonstrated similar flexibility last weekend, attending his nephew's Gloucestershire wedding before travelling to Epsom for the Derby.
King Charles's attendance at Lady Pamela Hicks's funeral remains uncertain amid a diary clash
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Pamela Hicks, Princess Alexandra of Kent, Princess Margaret and Queen Elizabeth as bridesmaids at the wedding of Patricia Mountbatten and Lord Brabourne in 1946
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GB News has contacted Buckingham Palace for comment.
Lady Pamela was the last surviving great-great-grandchild of Queen Victoria at the time of her death, connecting her by blood to virtually every royal house across Europe.
Born Pamela Carmen Louise Mountbatten, she was the younger daughter of Admiral of the Fleet Earl Mountbatten of Burma, the renowned wartime commander who was assassinated in 1979.
Her father's lineage made her a first cousin to the late Prince Philip, and through her paternal grandmother, Princess Victoria of Hesse, she was also a grandniece of Alexandra Feodorovna, the last Russian Tsarina.
Trooping the Colour is set to take place at Buckingham Palace on June 13
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Her connection to the late Queen Elizabeth II was particularly close, having served as one of the bridesmaids when the then-princess married Prince Philip on November 20, 1947.
Lady Pamela subsequently became a Lady-in-Waiting to the Queen, accompanying her on an extensive Commonwealth tour in 1953 to 1954 that took in Jamaica, Panama, Fiji, Tonga, New Zealand, Australia, Ceylon, Aden, Libya, Malta and Gibraltar.
She was present at a pivotal moment in royal history, standing alongside Princess Elizabeth in Kenya in February 1952 when news arrived of King George VI's death, marking the young princess's accession to the throne.
Born in Barcelona on April 19, 1929, Lady Pamela was christened at the Chapel Royal, St James's Palace, with an illustrious array of godparents including King Alfonso XIII of Spain and Prince George, Duke of Kent.
Lady Pamela Hicks attending Queen Elizabeth II's funeral in 2022
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Lady Pamela Hicks pictured with a walking stick in 2017
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She married interior designer David Nightingale Hicks at Romsey Abbey in January 1960, and the couple had three children: daughters Edwina and India, and son Ashley.
Lady Pamela also served as Corps Commandant of the Girls' Nautical Training Corps from approximately 1952 to 1959.
Her mother, Edwina Ashley, was the granddaughter of the immensely wealthy financier Sir Ernest Cassel.