A representative for Kate confirmed the separation to People, revealing the couple had been living apart for "some time" but remained amicable.
"Kate and Matt have been separated for some time now. Despite this, they remain very close friends and committed co-parents," said the spokesperson.
Oscar-winning actress Kate, 35, and English musician Matt, 36, became parents to son Bingham Hawn Bellamy on 9 July 2011.
Kate and Matt became engaged shortly before the birth of their son, with Kate confirming the news during a live TV interview when the journalist remarked on her huge ring.
"It just happened a week ago!" she said. "I'm so glad you noticed. I haven't really announced it. I was waiting for someone to notice!"
Almost Famous actress Kate and Matt proved their amicable status by walking the red carpet together on 21 November. They posed alongside Kate's mum Goldie Hawn at Goldie's inaugural Love In For Kids event in LA.
Kate is also mum to son Ryder, ten, from her marriage to Black Crowes frontman Chris Robinson.
Reveal is now on Google Plus! Join us here for the latest pictures, fashion and celebrity news!