King Charles and Queen Camilla received a special papal blessing to mark their 20th wedding anniversary during a private audience with Pope Francis in April.
The royal couple's meeting with the late pontiff was a significant gesture, given the Catholic Church's position on remarriage after divorce.
According to Robert Hardman's revised biography of the monarch, the King and Queen's meeting with Pope Francis lasted 20 minutes and took place behind closed doors.
During the encounter, the King and Pope prayed together, potentially marking the first such prayer between a Supreme Governor of the Church of England and a pontiff since Henry VIII's break with the church in 1534.
The meeting marked a watershed moment in relations between the Church of England and Rome. Hardman noted that the late Queen Elizabeth II encountered four popes during her reign, but never prayed alongside them.
"It might have been a short prayer, with the frail Pope in his chair and the King, alongside the Queen, on his feet. But it was a post-Henry VIII landmark," Hardman wrote.
Following Pope Francis's death just 12 days after the meeting, King Charles issued a message of condolence, remembering the pontiff's compassion, concern for the unity of the Church, and commitment to the common causes of all people of faith.
The King also recalled his meetings with Pope Francis, saying, "The Queen and I remember with particular affection our meetings with His Holiness over the years and we were greatly moved to have been able to visit him earlier in the month."
Prince William represented the King at the funeral mass of Pope Francis, paying tribute to the late pontiff's legacy and commitment to faith.