Kate Middleton's secret message to friends laid bare

Kate Middleton, who's currently undergoing chemotheraphy following her cancer diagnosis, once left her friends in shock with a secret message to them.

Kate, who made headlines for her whirlwind romance with Prince William years before their wedding in 2011, had already been preparing for a more formal change to her moniker. 

According to royal biographer Robert Jobson’s latest book, Catherine, the Princess of Wales, Kate sent an email to her friends asking them to call her Catherine instead of the more informal Kate.

Kate's message left pals in shock as it "added to the speculation" that William was going to propose her, according to Jobson.

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."

However, the author was not sure 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."

Prince William and Princess Kate, who are now parents of their three sweet kids - Prince George, Princess Charlotte and Prince Louis - are said to be planning big holiday plans this summer as the royal family traditionally gather at the late Queen's favourite Balmoral castle to spend holidays.