Nicole Kidman says motherhood has given her a "reason to live"

Asked how motherhood has changed her, she said: "I've been doing it for so long, and it's given me patience, a reason to live at times, and a reason to get up in the morning. So from the deepest part of who I am, it has given me purpose and the desire to stay around to see them into their adult lives, to protect them and to guide them. It's proven to me that there is unconditional love, it's shown me my resilience and given me the deepest sense of what it is to take care of another human being. To be willing to die for that other human being."

Despite her and Keith's fame, Nicole insists their family life is incredibly "normal".

She said: "It's as normal as can be, simple and loving. I have a very close relationship with my mum and my sister, and then an incredibly tight family.

"It's just normal. We go on the tour bus, we travel around, we have dinner together pretty much every night.

"I married my best friend and we get to raise these little girls - that is a gift and I will never take it for granted."

The 48-year-old star formed a strong friendship with her 'Big Little Lies' co-stars, Reese Witherspoon, Zoe Kravitz and Shailene Woodley, and though filming has long since finished, they are still in regular contact via a text group.

She told Glamour magazine: "We chat about being tired, love, balance, health, parents, mothers, kids, boyfriends, husbands, out pasts, and we help each other with advice, financial and emotional.

"One of the biggest things is saying, 'How much do you pay for this?'

and 'What would you do in this situation?' We are very open.

"We have all been through a lot, even Shai and Zoe."