Nicole Kidman and Keith Urban are one of the longest-lasting marriages in Hollywood.

The actress, 57, and the country singer, 56, have been married for 18 years and share two daughters – Sunday Rose, 15, and Faith Margaret, 13.

While interviewing her friend Victoria Beckham – who is celebrating her 25th anniversary with David Beckham – for Vogue Australia, the Oscar winner shared the  best piece of relationship advice she’s ever received.

‘The greatest advice I was given was there’s the individual – so there’s the me and the you – and there’s the we. And that’s only you,’ she revealed.

The Big Little Lies Star continued:  ‘No one else has what you two create, or what Keith and I create, any married couple who are partners, any people who have chosen to be in a relationship together, we create this, so we decide what this is.’

She added: ‘If you really like the person–really love them, but really like them, too, god it helps.’

The A Family Affair actress also stressed the importance of compromise – a good rule to follow in any relationship whether romantic or platonic.

‘Compromise as well. A lot. It’s always trial and error, and sometimes it’s imbalanced and then it gets back in balance…We don’t gloat about it.

‘People always ask, “What’s your marriage advice?” We don’t have any! Everyone does their own thing and creates it. I’m not some relationship guru. I’m just trying to find my own way,’ Kidman said.

The Big Little Lies actress continued talking about what a healthy relationship is while sounding very much like a wise therapist.

‘Normal emotions of fear and insecurity – you don’t have to push them down or deny them. They can be there, but you can work through them.

‘That’s what I say to my daughters: there’s a lot going on behind closed doors. But you’ve got to always go, am I able to push through the discomfort? Because the expectation of everything being wonderful all the time–it just doesn’t exist.

‘There will be many things that happen in a journey together and it’s beautiful and that is okay,’ she concluded.

Nicole, Keith and their daughters spent time together as a family at the Paris Olympics this week.

The foursome were among the fans who cheered on the women’s finals of Artistic Gymnastics in the Olympics on Tuesday.

The Kidman-Urban family were cheering on American gymnast Simone Biles who participated in the final as part of the US team.

Smiling for a group selfie, the parents and daughters appeared thrilled among other spectators.