Prince William and Kate Middleton separated before they got engaged and married.

Jessica Jayne revealed in her book, "Duchess of Cambridge: How Kate Middleton Became A Future Queen," that the Duke and Duchess of Cambridge decided to part ways because Prince William began to feel "claustrophobic" in his relationship with Middleton (via Express). Prince William flew to Greece with his friend Guy Pelly for some space which only made Middleton feel miserable.

The Duchess of Cambridge reportedly "never thought highly of" Pelly and deemed him as a "bad influence" on Prince William. Middleton packed her bags to spend the summer with her family.

In the same book, Jayne revealed that Middleton "let her guards down" around her friends. She was torn whether she text or call Prince William.

"She got quite drunk on white wine and really let her guard down. She was debating whether or not she should text or call him," one of Middleton's friends said. "She said how sad she was and how much she was missing William but she never mentioned it after that."

However, in their engagement interview, the couple revealed that they split because they were still figuring out what they want for themselves. Prince William believed their age was a factor.

"We were both very young," Prince William said. "It was at university, we were sort of both finding ourselves as such and being different characters and stuff, it was very much trying to find our own way and we were growing up."

Middleton admitted that she was hurt with the split, but it made her stronger. She also pointed out the realizations she had during that time.

"I think I at the time wasn't very happy about it, but actually it made me a stronger person," Middleton said. "You find out things about yourself that maybe you hadn't realised. Or I think you can get quite consumed by a relationship when you are younger."

Prince William and Middleton got engaged in 2010 and married in 2011. The couple is now parents to three adorable royal babies, 5-year-old Prince George, 3-year-old Princess Charlotte and 6-month-old Prince Louis. Betting odds suggest that the Duke and Duchess of Cambridge's fourth baby is "certainly a possibility"