The coronation of King Charles III will be held on May 6.
According to the Liturgy of the Coronation Service, the Prince of Wales will pledge his loyalty and allegiance to the King during the ceremony at Westminster Abbey on May 6. William, 40, the heir to the throne, will kneel before his father -- after he is officially crowned -- place his hands between the king's and recite the words, also known as the Homage of Royal Blood.
"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."
William is the only royal who will honor the King in this way during the ceremony. A role for Prince Harry was not listed.
The last time the words were uttered during a coronation was in 1953, during Queen Elizabeth II's ceremony. At the time, her husband, Prince Philip, made the vow and committed to being her "liege man of life and limb."
William will also be on hand to assist the Baroness Merron and the bishops in putting the robe on the King.
Also playing a role in the day is William and Kate Middleton's oldest son, Prince George. The 9-year-old's role as one of the King's pages of honor marks the first time in modern history that a royal who is a future monarch is involved in the service.
George, second in line to the throne, is the youngest future King to have a role in the ceremony.
A Kensington Palace spokesperson told ET, "We’re all very excited about Prince George’s role in the Coronation. It will be an incredibly special moment."
Joining George on the King's side as pages of honor are Lord Oliver Cholmondeley, Master Nicholas Barclay and Master Ralph Tollemache. Meanwhile, the Queen Consort’s pages of honor will be Her Majesty’s grandsons, Master Gus and Master Louis Lopes and Master Freddy Parker Bowles, and Her Majesty’s great-nephew, Master Arthur Elliot.
The pages will join the King and Queen throughout the service, and the pages will form part of the procession through the Nave of Westminster Abbey.