Kate Middleton's friends knew Prince William's proposal was coming after she made this request

When Prince William proposed in 2010, after about eight years of dating (with a brief break in 2007), Kate Middleton was already a globally recognized name. 

However, she had been getting ready for a more official change to her name. 

While the public knew her as Kate, and her friends used the same nickname, royal biographer Robert Jobson reveals in his latest book, Catherine, the Princess of Wales, that Kate sent an email to her friends asking them to refer to her as Catherine instead of the informal Kate. 

This "only added to the speculation" that William was going to propose, Jobson writes.

Jobson references a 2008 article by Sunday Express columnist Adam Helliker, which revealed that Kate had sent “a humorous email to her close friends” indicating her preference to be called Catherine.

According to Jobson’s new book, Helliker wrote, “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.”

In his new book, released on August 6, Jobson notes that it’s uncertain whether Kate disliked the nickname or if “it was part of a bigger preparation for her formal public role as Prince William’s future wife," adding that she seemed to have “a genuine desire to go by her full name.”

The name change happened in 2008, two years before William eventually proposed. 

However, "Inevitably all this led to a flurry of speculation about a potential royal title in the future,” though Prince Charles’ communications secretary, Paddy Harverson, “flatly denied” that notion, Jobson adds.