King Charles III: New Title Confirmed by Clarence House

The death of Queen Elizabeth changes everything for her eldest son.

The U.K.'s longest-reigning monarch died peacefully at age 96 at Balmoral Castle Thursday, making Prince Charles king, effective immediately. The 73-year-old royal will now be known as King Charles III.

Newly-elected Prime Minister Liz Truss also referenced the royal by the new title.

"Today the Crown passes — as it is has done for more than a thousand years — to our new monarch, our new head of state: His Majesty King Charles III," the prime minister said in part.

"With the King's family, we mourn the loss of his mother. And as we mourn, we must come together as a people to support him. To help him bear the awesome responsibility that he now carries for us all," Truss continued. "We offer him our loyalty and devotion just as his mother devoted so much to so many for so long. And with the passing of the second Elizabethan age, we usher in a new era in the magnificent history of our great country, – exactly as Her Majesty would have wished – by saying the words… God save the King."

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RELATED: Queen Elizabeth, the Longest-Reigning British Monarch, Dies at 96

Charles isn't the only member of the royal family to receive a new title. His wife, Camilla, Duchess of Cornwall, will also now be styled as Queen Consort, an honor Queen Elizabeth directly expressed her wishes for in February.

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In a message released on the eve of the 70th anniversary of her becoming monarch, Queen Elizabeth said that "when, in the fullness of time, my son Charles becomes King, I know you will give him and his wife Camilla the same support that you have given me; and it is my sincere wish that, when that time comes, Camilla will be known as Queen Consort as she continues her own loyal service."

Dominic Lipinski-WPA Pool/Getty Images Camilla, Duchess of Cornwall and Prince Charles

The new ranks were reflected in official communications from Buckingham Palace Thursday.

"The Queen died peacefully at Balmoral this afternoon. The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow," a statement said.

Charles was also referenced as "His Majesty, the King" on letterhead from Buckingham Palace, in his first statement as monarch following the death of his mother.

"The death of my beloved Mother, Her Majesty The Queen, is a moment of the greatest sadness for me and all members of my family," King Charles said.

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"We mourn profoundly the passing of a cherished Sovereign and a much-loved Mother," he continued. "I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world."

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"During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which The Queen was so widely held," the King concluded.

Upon his ascension in the royal line of succession, Charles follows his mother's lead in keeping his own first name as monarch.