They had been together four years and became engaged in April 2011, with son Bingham born just a few months later that July. The couple never wed.
"Kate and Matt have been separated for some time now," Hudson's rep told People magazine. "Despite this, they remain very close friends and committed co-parents."
After being engaged for such a long time, Hudson, 35, was often asked why she and her rocker fiance had never tied the knot.
Hudson explained on "The View" in July she felt married, living with Bellamy and their son, along with Ryder, 10, her son from a relationship with Black Crowes singer Chris Robinson.
"I'm happy, we're married," she said of her relationship of more than four years. "We've got kids and a family. ... We are in it. I think if we do get married it will be for the kids really."
She continued, "We're happy and ... we'll get there when we get there."
"I come from an unconventional family; they're not married, my parents aren't married," she said.
Hudson was married before to singer Robinson and the two split in 2006.
A request for comment from Hudson's rep was not immediately returned to ABC News.