The Prince of Wales and heir to the throne will step up at the ceremony to pledge his loyalty to his 74-year-old father. Following his crowning, William will kneel before the King while holding his hands in between the hands of Charles.
"I, William, Prince of Wales, pledge my loyalty to you and faith and truth I will bear unto you, as your liege man of life and limb. So help me God," the 40-year-old will say.
The specific words, titled the Homage of Royal Blood, pull from the words that William’s late grandfather, Prince Phillip, said in his 1953 vow to Queen Elizabeth to which he stated he’d be her "liege man of life and limb."
The father-of-three’s role was announced through the liturgy of the coronation service that the office of the Archbishop of Canterbury at Lambeth Palace recently released.
William will be the only member of the royal family to recite these ceremonial words before his newly-crowned father. Charles’ oldest son will also participate as the Stole Royal at Saturday’s service, meaning that he will help the Baroness Merron and bishops robe the King.
Additionally, the liturgy mapped out a significant change in the historic event. The Archbishop, Justin Welby, will invite the people of the U.K. to say the Homage of the People, which in the past was reserved for the dukes and earls present at the service.
The Church announced this will be a "new and significant moment in the tradition of the Coronation . . . As never before has the general public been offered such an opportunity to join with national figures in declaring their allegiance to the Sovereign."
"I swear that I will pay true allegiance to Your Majesty, and to your heirs and successors according to law. So help me God," the homage reads. "God save King Charles, Long live King Charles, May The King live forever."
In another break from tradition, leaders from the Jewish, Hindu, Sikh, Muslim and Buddhist faiths will speak to the King in unison as he leaves.
"As neighbors in faith, we acknowledge the value of public service. We unite with people of all faiths and beliefs in thanksgiving, and in service with you for the common good," they will say.