The double Major champion had been seeing the Danish tennis superstar for three years, and the duo got engaged on New Year's Eve.
But the 25-year-old golf sensation released a statement on Wednesday breaking the news that he and his girlfriend - both of whom are former world number ones in their respective sports - have split up.
"There is no right way to end a relationship that has been so important to two people," McIlroy said in his statement.
"The problem is mine,' he said.
"The wedding invitations issued at the weekend made me realise that I wasn't ready for all that marriage entails.
"I wish Caroline all the happiness she deserves and thank her for the great times we've had.
"I will not be saying anything more about our relationship in any setting."
The pair first got together in 2011, and instantly became the sporting world's favourite celebrity couple.
They frequently attended each other's events, with McIlroy once leaping out from the stands to take part in one of Wozniacki's exhibition matches, and Wozniacki famously caddying for her boyfriend at Augusta's pre-tournament par-3 tournament in 2013.
The pressure of conducting their relationship in public often seemed to take its toll, with regular reports that they had hit rocky patches.
Both stars also suffered slumps in form during their courtship, with Wozniacki in particular plummeting down the rankings - though McIlroy's 2012 US PGA Championship victory came after they had got together.
All the hoopla about their relationship often seemed to ignore the easily-forgotten fact that McIlroy is still only 25 years old, and Wozniacki just 23, and in the end it seems that the relationship simply ran its course.
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