The college sweethearts were on “different pages” before their ultimate engagement, according to the new biography ‘Catherine, The Princess of Wales’.

College sweethearts Kate Middleton and Prince William have been married for 13 years, but their royal relationship didn’t come without a few bumps in the road.

In Robert Jobson’s new biography Catherine, The Princess of Wales, the author looks back at the Prince and Princess of Wales’ romance after they graduated from the University of St. Andrews in 2005. Prince William, now 42, visited Kate, also 42, at her family’s home every Friday amid his military training at Sandhurst, and Kate was invited to her boyfriend’s military graduation in December 2006 — signs that their relationship was serious and might be heading toward an engagement.

Despite media attention on the topic and receiving the nickname “Waity Katie,” “Catherine knew William wasn’t in any hurry to propose, and the truth is she was prepared to wait until he was ready. After all, they were in love — weren’t they?” Jobson writes, according to an excerpt published by The Daily Mail on July 28.

However, Prince William canceled New Year’s plans in 2007, giving Kate the sense that “something was wrong.”

Soon after, Prince William called his girlfriend to break up, saying they both needed “a bit of space” to “find our own way” and that he was not able to promise a proposal.

“In an emotionally charged 30-minute conversation, they both acknowledged they were on ‘different pages,’ ” according to Jobson’s book. “It was a devastating blow to Catherine, who felt doubly let down at being dumped over the phone.”

While Prince William marked the split with a night out at Mahiki nightclub in London, Kate — who “resolved to hide her pain from the outside world” despite being “distraught” — took a break from the media with a trip to Dublin with mother Carole Middleton before a vacation in Ibiza with a friend. When she returned to London, Kate and her sister Pippa were often spotted leaving clubs — and photos would make their way into the press for William, who was spending most of his time in barracks as an army officer, to see.

Prince William was said to be having “second thoughts,” and the pair reunited at a “Freakin Naughty”-themed costume party thrown by jockey Sam Waley-Cohen.

“She’d arrived dressed as a nurse, and William had made a beeline for her,” Jobson writes. “They then spent the first part of the evening deep in conversation before hitting the dance floor, where they ended up kissing.”

Their romance continued from there, eventually moving in together before their engagement in 2010 and wedding the following year.

During their engagement interview, the future Prince and Princess of Wales spoke briefly after their break.

Prince William said, “We both were very young, 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, and so it was just sort of a bit of space and a bit of things like that and it worked out for the better.”

Kate added, “And I think I, at the time, wasn’t very happy about it, but actually, it made me a stronger person. You find out things about yourself that maybe you hadn’t realized, or I think you can get quite consumed by a relationship when you are younger, and I really valued that time for me as well although I didn’t think it at the time. Looking back on it.”

Prince William and Princess Kate are now parents to three children: Prince George, 11, Princess Charlotte, 9, and Prince Louis, 6.

Elsewhere in Catherine, The Princess of Wales, Jobson says Kate has been a “calming influence” on the royal family.

Through her role as an “instinctive peace-maker,” she has “smoothed the way for William and his father to have a better relationship than they had in the past,” Jobson says in an excerpt published by The Daily Mail over the weekend.