In a funny letter, Kate Middleton requested that pals refer to her as Catherine rather than Kate
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.”
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.