King Charles is to become the first monarch in over 400 years to officially attend a Catholic funeral in Britain, following the death of the Duchess of Kent.
Katharine Kent, who died on Thursday aged 92, converted to Catholicism in 1994 – the first member of the Royal family to do so since King Charles II converted on his deathbed in 1685.
Her widower, the Duke of Kent, is Queen Elizabeth’s cousin and now the oldest member of the Royal family at 89.
A Requiem Mass will be held on September 16 at Westminster Cathedral, the largest Catholic Church in England and Wales.
Other senior royals to attend will include Queen Camilla, the Prince and Princess of Wales, while Prince Harry will decide in the coming days on whether he will attend.
The Duchess of Kent died at the age of 92 (Rebecca Naden/PA)
Catherine Pepinster is the former editor of the Catholic Weekly, and told the Sunday Times it would be a day of “great historical significance.”
“There were signs of rapprochement between the monarchy and the Catholic Church under Elizabeth II – she met many Popes – but was careful not to attend a Catholic Mass in this country.
“The King and the heir to the throne attending Mass in Britain – that is of an entirely different order. This is a huge step forward in ecumenical relations.”
Since King Henry VIII famously split from the Catholic Church in the 16th century over the Pope’s refusal to grant him a divorce from Catherine of Aragon, she added that British monarchs had been expected “to stand up for the Church of England and reject the Church of Rome.”
Although King Charles has attended Mass before, as the head of the Church of England he has never done so before in Britain.
Charles and Camilla during a private meeting with Pope Francis in Rome on April 9 (The Vatican/PA)
Most recently, Charles and Camilla met privately with Pope Francis and prayed with him in the days before his death.
As Prince of Wales, he also attended Pope John Paul II’s funeral in 2005.
In 1993, Queen Elizabeth II also attended the Catholic state funeral of King Baudouin in Brussels.
Speaking of her “fairly impulsive” decision to convert to Catholicism, the Duchess of Kent previously told the Daily Telegraph in 1997: “I am not going to pretend that it was anything to do with reading the Bible.
“It had a great deal to do with people I met…I do live guidelines, and the Catholic Church offers you guidelines.
“I have always wanted that in my life: I like to know what is expected of me.”
A notice is placed on the gates of Buckingham Palace in London announcing the death of the Duchess of Kent (Jonathan Brady/PA) 
The duchess shakes hands with the Archbishop of Westminster, Cardinal Basil Hume, after he had received her into the Roman Catholic Church (Martin Keene/PA)