"[Sam and I are] grown-ups at the end of the day, and however hard it's been for me, it's been equally hard for him. And we have a child together who we both love - and raising him together, jointly and without any conflict, is absolutely key. It's the only way to do it, and I've really learned that with Mia."
Kate also spoke of the challenge of keeping her emotions under control:
"As a woman, especially when you have children, one gets so good at soldiering on - almost too good. I probably had very few moments of allowing that sadness to emerge. I kept pushing it away, not even really sharing it a huge amount with friends. Because you know what it's like, as soon as you open that can of worms, it's so f***ing big, you wish you'd never taken the goddamn lid off."
It sounds like the actress is determined to stay upbeat despite the heartache though as she added:
"I feel that I'm just at the beginning of a new narrative, and it's incredibly exciting. It's complicated, I know, and uncertain - but it's where life happens, between the cracks. It can be a painful process, but I truly hope that never stops for me."
The full feature appears in the November issue of Harper's Bazaar UK, on sale Thursday 6th October