King Charles' cousin, Lady Sarah Chatto, was among the guests to attend the thanksgiving service for the late King Constantine at St George's Chapel in Windsor.
The daughter of the late Princess Margaret, 59, was pictured arriving along with her husband, Daniel Chatto, as well as the Princess Royal, Mike and Zara Tindall and Princess Beatrice.
Lady Sarah, who is an artist and painter, was dressed respectfully in a dark coat and a turtleneck dress.
She wore her hair up in a low bun and accessorised with a simple diamond and sapphire brooch.
Lady Sarah and her brother, David, 2nd Earl of Snowdon, have always shared a close relationship with their cousins, King Charles and Princess Anne.
The pair grew up at Kensington Palace and David was first educated alongside his cousin, Prince Andrew, at the Buckingham Palace schoolroom before attending several independent schools.
Lady Sarah often joins the royals at major events, including King Charles' coronation, the annual Easter Sunday service in Windsor and Royal Ascot.
She and her husband, Daniel, and their sons, Samuel and Arthur, also attended the Christmas Day church service at Sandringham.
Lady Sarah married British artist and former actor Daniel Chatto on 14 July 1994 at St Stephen's, Walbrook in the City of London. Zara Tindall was among the bridesmaids.
There was a huge royal turnout at the service for the late King Constantine, former King of Greece, who died at the age of 82 in January 2023.
Queen Camilla led the British royals at the ceremony, including the Duke of York, Sarah, Duchess of York, the Duke of Kent, the Duke and Duchess of Gloucester, Prince and Princess Michael of Kent and Princess Alexandra.
They were joined by members of the Greek and Spanish royal families, including Constantine's widow, Queen Anne-Marie, and their children, Crown Prince Pavlos, Princess Alexia, Prince Nikolaos, Princess Theodora, Prince Philippos, and a number of their grandchildren.
The Prince of Wales missed the memorial service for his godfather Constantine because of a personal matter.
Kensington Palace would not elaborate further but said the Princess of Wales, who is recovering from abdominal surgery, continues to be doing well.
William called the Greek royal family to let them know he was unable to attend, and Crown Prince Pavlos stood in for the British heir to the throne who was due to give a Bible reading.