The 'Blurred Lines' hitmaker, 36, began dating Patton, 38, when he was 14. The high school sweethearts have been together for 22 years and welcomed their first child, son Julian, in April, 2010.
The couple confirmed the news to People magazine, saying: "We will always love each other and be best friends, however, we have mutually decided to separate at this time."
And, while the decision has left some people shocked, others have said it's been a long time coming.
A number of reasons have been suggested, with the naked girls in the 'Blurred Lines' video possibly being a trigger.
The infamous Miley Cyrus VMAs twerking incident may also not have gone down too well at home, while there was also a photo at a VMA after party showing Robin apparently grabbing a mystery girl's bottom.
What's more, there was reportedly an incident at trendy Paris nightclub, Club 79, where Rob did a little too much bump and grinding on the dance floor.
Whatever the reasons, after such a long time together, that's sad news for a Tuesday morning.