Queen Elizabeth II’s eldest son Charles became king immediately upon her death Thursday afternoon at Balmoral Castle in Scotland.

Within 24 hours of a monarch’s death, a new sovereign is proclaimed formally as soon as possible at St. James’s Palace in London by the “Accession Council,” according to the British monarchy's rules.

However, it may be months or even longer before Charles’ formal coronation. In Elizabeth’s case, her coronation came on June 2, 1953 -- 16 months after her accession on Feb. 6, 1952, when her father, King George VI, died.

In a statement issued by His Royal Majesty following the 96-year-old monarch's death, King Charles III said his mother's passing “is a moment of the greatest sadness” for him and his family.

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

Britain's new prime minister Liz Truss offered the King her "loyalty and devotion" in a statement acknowledging his role as the new monarch.

"Today, the crown passes, as it has done for more than a thousand years to our new monarch, our new head of state, his majesty King Charles III," Tuss said. "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 bears for us all. We offer him our loyalty and devotion, just as his mother devoted so much to so many for so long."

Charles' former title, the Prince of Wales, will now likely be passed to his son, Prince William, the Duke of Cambridge.

Born on the royal estate at Sandringham on Nov. 14, 1948, the first child of Princess Elizabeth and Prince Philip was formally invested as Prince of Wales and successor to throne on July 1, 1969.

As the heir to Britain's longest-serving monarch, Charles has been preparing for this moment most of his life.

Even as Britain celebrated the queen’s Platinum Jubilee in June, the 73-year-old Charles was taking on more public roles, often accompanied by his wife, Camilla.

With Elizabeth increasingly frailer in her last year, Charles often became the face of the monarchy, and earlier this year, presided over the State Opening of Parliament, one of the sovereign's most important duties.

“Prince Charles is the longest-serving heir we’ve ever had,” Robert Hardman, author of “Queen of Our Times: The Life of Elizabeth II” said. He was on standby to do whatever the queen could not, Hardman said.