New details from Kate by Michael O'Mara explain the couple's rough patch over six years ago.
The book claims that Prince William's partying ways with "glamorous half-naked girls," was one of the reasons that the couple decided to go their separate ways.
O'Mara says that Middleton had enough after seeing photos of William posing suggestively with women at numerous parties.
Aside from what initially caused the time off, the book also outlines what each of them did during their time apart.
The book says that Middleton kept busy during the split by visiting art exhibits with her close friends and travelling with her mother.
Meanwhile, William managed to get through the difficult time by focusing on his royal duties like charitable work and appearances.
The two reconciled months later and took their relationship to the next (and official) level by wedding four years later.
After two years of marriage, the happy twosome are about to add a third member to their household.
While we don't know whether they'll be welcoming a little boy or a little girl, Buckingham Palace confirmed their baby-to-be's official title: His or Her Royal Highness the Prince or Princess of Cambridge.
Considering the fact that dad and mom are the Duke and Duchess of Cambridge, it's not exactly a shocker that their little one should take the title. What is unique, though, is that this royal baby will be the first ever Prince or Princess of Cambridge.
And the entire world is on royal baby watch! The child is, after all, the future king or queen of England. Thanks to an October 2011 change to the rules of royal succession, William's firstborn son or daughter is eligible to become the future heir to the throne.
"Put simply, if the Duke and Duchess of Cambridge were to have a little girl, that girl would one day be our queen," British Prime Minister David Cameron explained.