The 45-year-old actress - who adopted two children with the 'Mission Impossible' star before they parted ways in 2001 - blames getting married at the young age of 23 for spiraling into depression after her divorce, even though she has no regrets about their relationship.
Nicole said: "I got married really fast and really young. But I don't regret that because it got me Bella and Connor and I did have a fantastic marriage for a long period.
"Then when it didn't work out I had to really dig deep and find my way through depression. I have no regrets about all of it. It was all part of growing up."
The flame-haired beauty is now happily married to country singer Keith Urban, with whom she has biological daughter Sunday Rose, four, and 22-month-old Faith, born to a surrogate mother.
The 'Australia' actress admitted being unable to conceive naturally had a huge impact on her depression and she was left devastated by a series of miscarriages and failed IFV treatments until her "miracle" daughter came along.
Nicole added to Who magazine: "I had so much time thinking that wasn't going to happen in my life and trying to understand that. When it did happen - and for it to be a surprise - hat was great.
"I had tried and failed and failed and failed. Not to be too detailed, but I've had an ectopic pregnancy, miscarriages and I've had fertility treatments. I've done all the stuff you can possibly do to try get pregnant.
"Every woman who has been through all those ups and downs knows the depression that comes with it. So the way it just happened with Sunday was like, 'What?' The percentages were so low. It is the miracle in my life."