Kate Middleton and Prince William's New Royal Titles Just Became Official — Here's Why

Prince William and Kate Middleton's titles as the Prince and Princess of Wales are now official.

Just one day after the Sept. 8, 2022, death of Queen Elizabeth II, King Charles III gave his first speech as the United Kingdom's monarch. In the televised broadcast, the new sovereign announced that his son Prince William would be the new Prince of Wales and his daughter-in-law Kate would become the Princess of Wales.

However, the royal titles only became official this month, when the Letters Patent passed the Great Seal of the Realm on Feb. 13. The full notice from the Crown Office was printed in The Gazette on Friday.

Chris Jackson/Getty Prince William and Kate Middleton at the BAFTAs 2023

The announcement read in full: "In accordance with the direction of HIS MAJESTY THE KING Letters Patent have passed the Great Seal of the Realm, dated the 13th February 2023 for creating His Royal Highness Prince William Arthur Philip Louis, Duke of Cornwall Rothesay and Cambridge, Earl of Carrick and Strathearn, Baron of Renfrew, Baron Carrickfergus, K.G., K.T., Lord of the Isles and Prince and Great Steward of Scotland, PRINCE OF WALES and EARL OF CHESTER."

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Chris Jackson/Getty Queen Camilla, King Charles, Prince William and Kate Middleton

Prince William, 40, and Kate, 41, were given the titles of the Duke and Duchess of Cambridge by Queen Elizabeth on their wedding day in 2011. When they were proclaimed the Duke and Duchess of Cambridge, the couple simultaneously became the Earl and Countess of Strathearn as well as Baron and Baroness of Carrickfergus, although those titles were used less often.

Immediately following the death of Queen Elizabeth, William and Kate's Twitter and Instagram accounts were updated to state they belonged to the "Duke and Duchess of Cornwall and Cambridge," as the title of the Duke of Cornwall is traditionally held by the eldest son of the reigning British monarch, with his wife taking the Duchess title. Prince William and Kate also became the Duke and Duchess of Rothesay, titles previously used by Charles and Camilla, applied when they are in Scotland.

William and Kate retained their Cambridge titles.

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EDDIE MULHOLLAND/POOL/AFP via Getty Prince William and Kate Middleton

However, the Prince of Wales title is not automatic and must be bestowed by the monarch.

The legal instruments known as letters patent are an open document from the monarch used to express the sovereign's will, such as "to confer an office or create a new peerage," according to the Royal Collection Trust. Now, the letters patent making Prince William the Prince of Wales passed the Great Seal of the Realm.

Along with becoming the Prince of Wales, the letters patent also decreed that William is granted the title of Earl of Chester. That makes Kate the Countess of Chester.

Hulton Archive/Getty July 1, 1969: Queen Elizabeth II crowns her son Charles, Prince of Wales, during his investiture ceremony at Caernarvon Castle

Charles, now 74, was just 3 when his mother, Queen Elizabeth, acceded to the throne. He was not formally pronounced the Prince of Wales until he was 9, and the Investiture of the Prince of Wales — when Charles was presented to the Welsh people as their prince — took place at Caernarfon Castle in 1969 when Charles was 20.

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Such a ceremony is not expected to take place for Prince William, but he will likely play a role in King Charles' coronation on May 6.