Talking of the couple's break up, a close friend told the Daily Mail at the time: "He is only 24 and simply wasn't ready to settle down.
"He has always had a roving eye [...] that's something Kate had always known and accepted - it was part of the deal, if you like."
The source also revealed that "Kate did everything she could to make him stay" by "playing a waiting game one minute and then hard-to-get the next."
So when William was photographed partying with other girls in London nightclubs, Kate rebelled and punished the Prince in her own way.
The source said she told friends "she intended to be photographed at as many places as she could without William to punish him".
Despite the pictures of Kate out partying, she handled herself “brilliantly” according to former BBC royal correspondent Jennie Bond.
“She did not make a fool of herself and crucially she did not talk to the press,” Jennie Bond said.
They finally got back together a few months later, and were first spotted at the Concert for Diana in July 2007, which was hosted by Prince William and Prince Harry.
And by 2010 the couple had announced their engagement, with Prince William revealing in their interview with the BBC that he knew from the start that Kate was different from other people.
"From my point of view, when I first met Kate, I knew there was something very special about her,” he said in their engagement interview.
And when asked what brought them together, her “naughty sense of humour” was the tipping point.
He said: “She’s got a really naughty sense of humour, which really helps me because I’ve got a really dirty sense of humour so it was good fun, we had a really good laugh, and then things happened.”
The couple finally married at Westminster Abbey in London, on April 29, 2011. The ceremony was watched by royal fans across the world in more than 180 countries.