Special clause inserted into Nicole Kidman and Keith Urban's divorce agreement as they officially separate after 19 years

This is what the alleged 'cocaine clause' means in Nicole Kidman and Keith Urban's divorce settlement, which has officially been finalised.

Reports that the superstar couple had split after nearly two decades of marriage first emerged in September last year.

The Australian actress filed for divorce from country music star Urban three months ago, citing irreconcilable differences - and a judge in Nashville, Tennessee, has now signed off on it.

Judge Stephanie J. Williams granted Kidman and Urban's divorce at a hearing on Tuesday (6 January), after agreeing that their agreements over how to split their assets and child custody were sufficient.

According to court documents, the pair, who got hitched at a ceremony in Sydney in June 2006, both agreed to waive all child and spousal support rights, PEOPLE reports.

The Babygirl star and the 'Somebody Like You' singer, both 58, are also both responsible for their own legal fees and other expenses - and it appears that Urban hasn't cashed in on the so-called 'cocaine clause' that was reportedly included in their prenuptial agreement.

The couple, who got hitched in 2006, are now officially divorced (Francis Specker/CBS via Getty Images)

What is the 'cocaine clause'?

Before tying the knot, Urban struggled with drug addiction and alcoholism. Just four months into their marriage, Kidman was forced to stage an intervention for him, which Urban later described as a vital moment in turning his life around.

When appearing on The Zane Lowe Show, Urban said: "All through the years of drinking and doing drugs and all the rest of it, I always had this very specific voice inside of me that goes, 'One day, you're gonna come to a crossroads or a fork in the road, and it'll be the final one'."

"I knew that was it," he said in reference to marrying Kidman. "I'm like, ‘Oh, this is that fork in the road'. You're either gonna choose to get out of this s**t, or you're never gonna get out of it."

So, in their prenup, an alleged clause was included stipulating that if Urban remains sober from drugs and alcohol throughout their marriage, he will receive a payment of $600,000 for every year that they were together, once that relationship ends, per Radar Online.

But it seems he hasn't claimed the cash that the 'cocaine clause' was supposed to get him, due to it not appearing to be present in the finalised documents.

Kidman and Urban share two daughters together (Pascal Le Segretain/Getty Images)

Nicole Kidman and Keith Urban's plans to co-parent

Kidman and Urban share daughters Sunday Rose, 17, and Faith Margaret, 14, and some ground rules have been set in regards to how they are going to co-parent them.

A parenting plan states that the former couple must 'behave with each other and each child so as to provide a loving, stable, consistent and nurturing relationship with the child even though they are divorced'.

"They will not speak badly of each other or the members of the family of the other parent," it reportedly continues. "They will encourage each child to continue to love the other parent and be comfortable in both families."

Their teen daughters will spend 306 days out of the year with their mother, while Urban has 59 days, according to People. Both Kidman and Urban will share responsibility for major decisions in their daughters' lives, too, so all in all, it sounds quite the amicable separation.

Although their split seems to have remained civilised, Judge Williams said that the 'irreconcilable difference between the parties that would render continuation of the marriage impractical and impossible'.

In November last year, Kidman appeared to allude to the impact her split with Urban has had on her - while vowing to find 'a way through'.