The actress became engaged to Muse rocker Matt in 2011 – the same year they welcomed their son Bingham Hawn Bellamy – but announced their separation in December last year.
Speaking to Allure magazine, she said: "Relationships ending are painful, and you can choose to carry that or you can choose to reframe it. If Matt and I had a great relationship, we would still be together, but we chose to move on because we had different visions of how we wanted to live our lives.
"That doesn't mean, though, that we can't rebuild something that would be the best thing for the kids. We said, 'We need to try to create something for the kids where they feel like they're gaining something rather than losing something.'
"It's been a seamless transition. Kids just want to see their parents be cool. Everybody's cool; everybody's good."
Kate also has a son Ryder, 11, from her marriage to Chris Robinson.
In a tweet after the split news, Matt told fans: "Love all of you guys! We're both very happy, it's for the best. Thanks for your kind words. Now about that new album..."
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