"He found her too needy and it just wasn't working out," the publication cited a source close to the royal as saying.
Clarence House, the office of Harry's father Prince Charles, declined to comment.
"Cressy" and Prince Harry, fourth in line for the British throne, were first spotted together in July 2012.
According to People, they were introduced by Princess Eugenie, Harry's cousin, a friend of the 24-year-old beauty. The couple tried to keep their relationship out of the paparazzi spotlight.
In March, the two were seen in public twice in the span of a weekend, prompting the British press to speculate that things were getting serious.