By the time Prince William proposed in 2010 after roughly eight years together (save for a brief split in 2007), Kate Middleton’s name was known worldwide. However, she had already been preparing for a more formal change to her moniker.

In addition to the public knowing her as Kate, her friends called her by that nickname. However, according to royal biographer Robert Jobson’s latest book, Catherine, the Princess of Wales, Kate sent an email to friends asking them to call her Catherine instead of the more informal Kate, which “only added to the speculation” that William was going to propose, Jobson writes.

Jobson cites a 2008 article by Sunday Express columnist Adam Helliker that disclosed that Kate had written “a humorous email to her close friends” expressing her desire to be called Catherine.

Helliker wrote, per Jobson’s new book, “I hear that in the past few weeks, the former accessories buyer has quietly informed friends that she would like to drop the informal ‘Kate’ and in future wishes to be known by her full name: Catherine.”

Kate Middleton attends the Day-Glo Midnight Roller Disco in 2008.
Max Mumby/Indigo/Getty

Jobson writes in his new book, out Aug. 6, that it was unclear if she didn’t like being called Kate or whether “it was part of a bigger preparation for her formal public role as Prince William’s future wife,” adding that it appeared she “had a genuine desire to go by her full name.”

The name switch occurred in 2008, two years before William ultimately popped the question. But, “Inevitably all this led to a flurry of speculation about a potential royal title in the future,” although then Prince Charles’ communications secretary Paddy Harverson “flatly denied” that assumption, Jobson continues.

Kate Middleton and Prince William at their engagement announcement in 2010. Chris Jackson/Getty

The 2008 email to friends wouldn’t be the only time what to call the future Princess of Wales was debated.

Kate’s brother-in-law, Prince Harry, shared an anecdote about her moniker in his 2023 memoir, Spare, writing that King Charles once asked his daughter-in-law to change the spelling of her first name to Katherine with a “K” instead of with a “C”: “This was because there were already two royal cyphers with the letter C in them — and they didn’t want another,” the Duke of Sussex wrote, referring to not just Charles and his wife, Queen Camilla, who was known as the Duchess of Cornwall at the time.

“Make it Katherine with a K, they suggested,” Harry said in the book. The Duke of Sussex wrote that he spoke to his brother, Prince William, at the time about their father’s suggestion: “I turned to Willy, gave him a look that said, ‘You listening to this?’ His face was blank.”

Prince William, Kate Middleton and Prince Harry at Princess Eugenie’s wedding in October 2018. Owen Humphreys – WPA Pool/Getty

Queen Elizabeth granted Prince William and Kate the royal titles of the Duke and Duchess of Cambridge on their wedding day in 2011. However, King Charles announced they would be the Prince and Princess of Wales following his accession in 2022, giving his eldest son the traditional title of the heir to the throne.

According to experts at Debrett’s, a U.K. authority on etiquette and titles, she is properly styled as Catherine, Princess of Wales rather than Princess Catherine. Also technically correct: Princess William of Wales.

Prince William and the palace regularly reference her as Catherine in statements and formal communications, though the public and press colloquially call her Kate, as do some of her own friends.