What he feared at the time was that if their relationship went public, the paparazzi would go after Kate, and he didn’t want that because he was very protective of her.

However, during a ski trip, a photographer took a photo of the couple cozied up on the slopes and that photo appeared on the cover of a magazine the following day. Needless to say, this left William enraged.
“Unfortunately for them, a paparazzi photographer took pictures of William and Kate clearly very close on the ski lift together. A red top tabloid newspaper slashed it all over their front page,” royal expert Rebecca England said on Channel 5’s documentary William & Kate: Too Good To Be True. “William was furious, and he was also genuinely worried for Kate and her family about what this would now mean for them.”
And as everyone believed a royal marriage was just around the corner, the two split in 2007.

Recalling the time of their break up, both Kate and William claimed it was actually good for them because they got to “find themselves.” Kate even said that “you can get quite consumed by a relationship when you’re younger,” as per The Telegraph.
The two got back together in 2008 and William proposed to Kate in 2010 during a trip to Kenya with his late mother’s engagement ring.
Today, after three children and years of being together, William and Kate’s relationship is as strong as ever.