Details of the funeral arrangements for Katharine, Duchess of Kent, have been released as King Charles III and Queen Camilla prepare to attend what officials described as the first Catholic funeral for a member of the British royal family in modern history.

The duchess, who died on Sept. 4 at the age of 92, had converted to Roman Catholicism in 1994 and expressed a wish for her funeral to be held at Westminster Cathedral. In keeping with Catholic tradition, her coffin will be taken from Kensington Palace to the cathedral on Monday for a series of private funeral rites attended by immediate family. It is expected to lie overnight in the cathedral's Chapel of the Blessed Virgin Mary before a requiem mass on Tuesday, which the King, Queen and other senior royals will attend.

Officials said the coffin will be led for the first part of its journey by a military piper from The Royal Dragoon Guards, a regiment the duchess supported as deputy Colonel-in-Chief since its inception in 1992. Other service personnel from the regiment will form the bearer party carrying the coffin into the cathedral.

The arrangements mark several firsts. The duchess will be the first member of the royal family in more than 300 years to be given a Catholic funeral. The last Catholic monarch was King James II, who reigned until he was deposed in the Glorious Revolution of 1688; the Act of Settlement 1701 thereafter barred Catholics from the throne and ensured a Protestant line of succession. Westminster Cathedral, completed in 1903, has not hosted a royal funeral since its construction.

Royal officials said the King had approved a period of royal mourning to run until and including the day of the duchess's funeral. Members of the royal household and staff will wear clothing considered appropriate for the period, and those in Livery, the Royal Mews and troops on public duties will wear black armbands. A national mourning period is not expected, officials added, because the duchess had not been a working royal since 2002, although some public tributes are anticipated and royal engagements will continue with consideration given to their format and tone.

Tributes to the duchess highlighted her charitable work and long-standing ties within the royal family. The Prince and Princess of Wales said the duchess would be "much missed" and that she had "worked tirelessly" to help others. Prime Minister Keir Starmer described her as bringing "compassion, dignity and a human touch to everything she did." The duchess was known for a close friendship with the late Diana, Princess of Wales, and for supporting numerous causes, including through her interest in music.

Although the planned Catholic funeral is unprecedented in recent centuries for a royal, members of the royal family have attended Catholic services abroad and in recent decades. Queen Elizabeth II attended the Catholic funeral of Belgium's King Baudouin in 1993. Charles, as prince, attended Pope John Paul II's funeral in 2005, and the Prince of Wales attended Pope Francis's funeral mass earlier this year.

Officials said Monday's private rites will be attended by the duchess's immediate family and will follow Roman Catholic practice, while Tuesday's requiem mass at Westminster Cathedral will be a public liturgy marking her life and faith. The duchess had relinquished the royal style "Her Royal Highness" later in life, and her conversion to Catholicism in 1994 was one of the most notable personal decisions of her later years.

Further details of guest lists and the precise timing of the services were not immediately released. The royal household said it would provide additional information in due course as arrangements are finalised.