Prince Edward, the Duke of Edinburgh, is set to represent King Charles at the inauguration of Pope Leo XIV.
Prince William previously attended Pope Franics' funeral on behalf of the King due to a longstanding royal rule.
The inauguration Mass for the 267th Pontiff and Bishop of Rome will take place on the morning of May 18 at St. Peter’s Square.
American Robert Prevost, 69, was elected as new pontiff on May 8 following a a conclave of the Catholic Church's cardinals.
The King will not attend the inauguration of Pope Leo XIV
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The Chicago born churchman, the first American to be granted the role, succeeded Pope Francis, himself the first South American, after his death on April 21.
While he will not attend the Pope''s inauguration, King Charles sent a private message of congratulations to Leo upon his election.
"Peace be with you" were Pope Leo's first words as he addressed a crowd of thousands from balcony before St Peter's Square.
After thanking his predecessor Francis and praying for world peace, Leo said: "Evil will not prevail... We are all in the hands of God.
The Duke of Edinburgh will represent the King and Pope Leo's inauguration
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"Without fear, united hand-in-hand we go forward, we are disciples of Christ."
The crowd below was heard cheering "Leo, Leo", before the new Pope spoke of the need for God and Christ.
"The world needs his light, humanity needs him in order to be reached by God and his love. Let us build bridges through dialogue... to be one people in peace."
Following his accession to the role, others around the world shared public congratulations.
Pope Leo spoke to Catholics around the globe upon his election
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US President Donald Trump said it was "such an honour to realise that he is the first American Pope".
"I look forward to meeting Pope Leo XIV. It will be a very meaningful moment," Trump added.
The King's son, Prince William, marked the passing of Pope Francis in his place as the Sovereign does not attend funerals according to historic royal protocol.
The Argentinian former pontiff died on Easter Monday at the age of 88, triggering mourning among Roman Catholics worldwide.
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Prince William attended the funeral of Pope Francis
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Prince William, as the future leader of the Church of England, was seated among the non-Catholic royals in the second row.
The Prince of Wales sat with Crown Prince Haakon and Crown Princess Mette-Marit of Norway.
Catholic royals were positioned in the front row of St Peter's Basilica as they paid tribute to the late pontiff.
These include Prince Albert and Princess Charlene of Monaco, King Felipe and Queen Letizia of Spain and Grand Duke Henri and Grand Duchess Maria Teresa of Luxembourg.
