King Charles and Pope Leo XIV have become the first British monarch and pontiff to pray alongside one another in at least 500 years, during a session held inside the Sistine Chapel. (Supplied: Vatican News)

In short:

King Charles and Pope Leo XIV have prayed together in an historic service at the Sistine Chapel.

It is the first time in 500 years that a British monarch and pontiff have prayed together.

The pair have exchanged gifts and will confer honorary titles on the other during the visit.

King Charles and Pope Leo XIV have become the first British monarch and pontiff to pray together at a church service in at least five centuries.

The historic moment in the Sistine Chapel was planned as part of a royal visit to the Vatican by King Charles and Queen Camilla.

The king, who is the supreme governor of the Church of England, was seated at the pope's left near the altar of the chapel, as the pope and Anglican Archbishop Stephen Cottrell led the service, that was mainly in English but featured some singing in Latin.

Clergy and choirs from both the Catholic Church and the Church of England were brought together for the service, which was seen as a symbolic display of unity.

A spokesperson for King Charles said a stronger relationship between the two branches of Christianity was a "bulwark against those promoting conflict, division and tyranny".

King Charles, along with Queen Camilla, first met with the pontiff in a private discussion held at the Holy See. (Reuters: Supplied / Vatican Media)

The Church of England broke away from the Catholic Church during the 16th century, and became its own branch of Christianity.

While members of the royal family travelled to the Vatican on several occasions since, they had not engaged in public acts of worship with pontiffs.

King Charles and Queen Camilla's visit, which has seen their first meeting with Pope Leo, coincides with the papal jubilee, which is traditionally marked every 25 years.

King Charles and Queen Camilla were welcomed to the Vatican at the courtyard of Sam Damaso. (Reuters: Phil Noble)

Jubilees are considered years of forgiveness and renewal, though, in the Bible, they also involved the cancelling of debt and periods of rest.

The 2025 Jubilee was first announced by Pope John Paul II at the end of the 2000 Great Jubilee.

The monarch's visit comes amid an ongoing saga surrounding the king's brother, Prince Andrew, who has dominated headlines after giving up his royal titles and honours amid a series of scandals.

Pope Leo, King Charles and Queen Camilla (far right) following the service in the Sistine Chapel. (Supplied: Vatican Media)

Before praying together, the two leaders met in the pope's library and exchanged gifts.

King Charles gave the pope an Icon of St Edward the Confessor, a devout 11th century king of England.

Pope Leo gifted a scale version of a mosaic of Christ Pantocrator, which depicts Jesus in a Normal cathedral in Sicily. The mosaic was made in the Vatican.

Charles also met with Cardinal Pietro Parolin, the Holy See's Cardinal Secretary of State.

He was the first papal representative in 500 years to attend a British monarch's coronation when he attended King Charles's coronation at Westminster Abbey in 2023.

Queen Camilla wore a dark frock and head garment during her arrival to the Vatican. (Reuters: Phil Noble)

The king will travel in the afternoon to Rome's Basilica of Saint Paul Outside the Walls, where he will receive the new title of Royal Confrater, or brother, after Pope Leo approved the move.

A wooden chair will also be gifted to the monarch, which will be reserved for future use by British royalty, that has been decorated with the king's coat of arms.

Charles approved two British honours for Pope Leo on Thursday, making him the Papal Confrater of St. George's Chapel, Windsor Castle, and conferring on him the Knight Grand Cross of the Order of the Bath.

The birth of the Anglican tradition

For centuries, a rift has existed between the British monarchy and the Catholic Church.

It traces back to the first half of the 16th century, when Henry VIII was the king of England.

In 1527, Henry had been married to his first of six wives, Catherine of Aragon, for 18 years.

While they had six children over the years, only one daughter, Mary, lived past infancy.

King Charles III shares a name with two kings whose rules were marked by bloodshed and scandal.

Henry was frustrated with their inability to produce a male heir, arguing it was because their marriage was "blighted in the eyes of God".

To solve this problem, he wanted his marriage to Catherine annulled so he could wed another woman — Anne Boleyn.

Being a Catholic, he needed the permission of the head of the church to do so.

At the time, that was Pope Clement VII.

Possibly under pressure from Catherine's nephew, Holy Roman Emperor Charles V, the pope refused to grant Henry's annulment.

Henry's solution was for England to follow the example of Protestant campaigners in other parts of Europe and break away from the authority of the pope — a process known as the Reformation.

That sparked a campaign now known as the English Reformation, where the Church of England broke away from the authority of the pope.

Years later in 1534, Henry was declared the head of the Church of England — a move that formally severed ties with the Catholic Church.

From then, the Church of England was shaped by both the Catholic and Protestant traditions into its own branch of Christianity, known as Anglicanism.

Because of the distinctions between Catholicism and Anglicanism, popes and British monarchs no longer participated in religious practices together — until today. (ABC News)