The King and Queen have expressed their “most heartfelt condolences and profound sympathy” following the death of Pope Francis.

Charles and Camilla had a moving meeting with the ailing 88-year-old while he was convalescing just 12 days ago.

The couple’s historic state visit to the Vatican in early April was cancelled because of the Pope’s poor health, but they managed to visit the head of the Roman Catholic Church privately during their trip to Italy.

The King, in an official message released following the news of the pontiff’s death on Monday, said he and Camilla were “most deeply saddened”.

He praised Pope Francis for his compassion and tireless commitment to the common causes of all people of faith.

The Union flag will be flown half-mast at royal residences where Charles is not in residence as a mark of respect and in accordance with Government guidance.

Sombre music will played at the Changing the Guard ceremony to reflect “the sadness of the occasion”, a royal source said.

A member of the royal family is expected to attend the Pope’s funeral, if the Vatican is in agreement, but it is too early to say who will travel to pay their respects.

Royal engagements are likely to continue as planned, but will take into account any sensitivities regarding tone in the wake of Francis’s death.

The King said: “My wife and I were most deeply saddened to learn of the death of Pope Francis.

“Our heavy hearts have been somewhat eased, however, to know that His Holiness was able to share an Easter greeting with the Church and the world he served with such devotion throughout his life and ministry.

“His Holiness will be remembered for his compassion, his concern for the unity of the Church and for his tireless commitment to the common causes of all people of faith, and to those of goodwill who work for the benefit of others.

“His belief that care for Creation is an existential expression of faith in God resounded with so many across the world.

“Through his work and care for both people and planet, he profoundly touched the lives of so many.

“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.

“We send our most heartfelt condolences and profound sympathy to the Church he served with such resolve and to the countless people around the world who, inspired by his life, will be mourning the devastating loss of this faithful follower of Jesus Christ.”

Charles and Camilla’s meeting with the Pope in what would be his final weeks was arranged at the last minute and took place on their 20th wedding anniversary on April 9, with the pontiff wanting to personally wish them a happy anniversary.

A senior Palace official said afterwards: “I think outside of the official programme, the most significant and indeed moving thing was that visit to the Pope.

“We didn’t know until the last minute that it would be possible. But when the Pope asked if he could see the King and Queen, Their Majesties were clearly very pleased; after all, they have known him over many years and, with the rest of the world, have been praying for his recovery.

“The Pope wanted personally to wish them a happy anniversary, not least because it hadn’t been possible to do the state visit on this occasion.

“Their Majesties both came away feeling that it had been a very significant and special moment.”

Twenty years ago, Charles and Camilla’s marriage ceremony was postponed with just four days to go following the death of Pope John Paul II.

The then-Prince of Wales put duty first and his wedding date was moved from April 8 to April 9 2005 because it clashed with the pope’s funeral.

Charles represented the late Queen by travelling to Rome to attend the service, alongside more than 100 world leaders and ended up shaking hands with Zimbabwean president Robert Mugabe.

The then-archbishop of Canterbury, Dr Rowan Williams, who was due to conduct the prince’s blessing in St George’s Chapel in Windsor Castle after his civil ceremony had made it clear he wished to break with tradition and attend the pope’s funeral.