It’s the break-up that has shocked Hollywood.

After 19 years together, Nicole Kidman and Keith Urban have called it quits.

The Oscar-winning actor, 58, has filed for divorce from the Grammy-winning country singer, 57, citing ‘marital difficulties and irreconcilable differences.’

So, where did it all go wrong?

While every break-up is different, research could help to shed light on the real reason for the separation.

Four negative communication styles have been deemed so lethal to relationships that they’ve earned the title of the ‘Four Horsemen of the Apocalypse’.

According to research, they predict relationship failure with over 90 per cent accuracy.

So, could they help to explain why Nicole and Keith have called it quits?

The Four Horsemen theory was developed back in 1994 by Dr John Gottman, an American psychologist and professor emeritus of psychology at the University of Washington.

Dr Gottman recruited newlywed couples, who came into the laboratory to be studied, having spent the previous eight hours not talking to one another.

In the lab, the couples were filmed during three 15-minute conversations – one about the day’s events, one about conflict within the marriage, and one on an unpleasant topic.

The researchers then coded the footage for the presence of certain behaviours and emotional expressions.

Finally, the couples were contacted several years down the line to determine if they were still together or had separated or divorced.

Based on the analysis, Dr Gottman identified four key behaviours – dubbed the Four Horsemen of the Apocalypse – that indicate a couple is headed for a split.

1. Criticism

The first horseman is criticism, which the Gottman Institute describes as ‘an attack on your partner at the core of their character.’

Crucially, this is different from a complaint.

After 19 years together, Nicole Kidman and Keith Urban have called it quits. The Oscar-winning actor, 58, has filed for divorce from the Grammy-winning country singer, 57, citing ‘marital difficulties and irreconcilable differences’

For example, a complaint might be: ‘I was scared when you were running late and didn’t call me. I thought we had agreed that we would do that for each other.’

In contrast, criticism could be: ‘You never think about how your behavior is affecting other people. I don’t believe you are that forgetful, you’re just selfish. You never think of others! You never think of me!’

If this sounds familiar, don’t panic – thankfully, this doesn’t necessarily mean your relationship is doomed to fail.

‘The problem with criticism is that, when it becomes pervasive, it paves the way for the other, far deadlier horsemen to follow,’ the Gottman Institute explains.

‘It makes the victim feel assaulted, rejected, and hurt, and often causes the perpetrator and victim to fall into an escalating pattern where the first horseman reappears with greater and greater frequency and intensity, which eventually leads to contempt.’

2. Contempt

This takes us on to the second horseman – contempt.

‘When we communicate in this state, we are truly mean—we treat others with disrespect, mock them with sarcasm, ridicule, call them names, and mimic or use body language such as eye-rolling or scoffing. The target of contempt is made to feel despised and worthless,’ the Gottman Institute explained.

While criticism is an attack on character, contempt goes further by assuming a position of moral superiority over them.

According to the experts, contempt is the single greatest predictor of divorce.

3. Defensiveness

Defensiveness – typically in response to criticism – is the third horseman.

According to the Gottman Institute, defensiveness is ‘nearly omnipresent’ in relationships that are on the rocks.

‘When we feel unjustly accused, we fish for excuses and play the innocent victim so that our partner will back off,’ it explained.

Unfortunately, defensiveness is almost never successful, and simply implies to our partner that we don’t want to own up to our mistakes.

‘Defensiveness is really a way of blaming your partner, and it won’t allow for healthy conflict management,’ the Gottman Institute added.

The Four Horsemen theory was developed back in 1994 by Dr John Gottman, an American psychologist and professor emeritus of psychology at the University of Washington

4. Stonewalling

Finally, the fourth horseman in stonewalling, which is usually in response to contempt.

‘Stonewalling occurs when the listener withdraws from the interaction, shuts down, and simply stops responding to their partner,’ the Gottman Institute explained.

‘Rather than confronting the issues with their partner, people who stonewall can make evasive manoeuvres such as tuning out, turning away, acting busy, or engaging in obsessive or distracting behaviours.’

What can you do if you recognise one of the key signs that your relationship is heading for a breakup?

If the Four Horsemen are ringing alarm bells for you, thankfully experts say that there are easy ways to eliminate them in your relationship.

The antidote to criticism is ‘gentle start-up’, which involves starting complaints with ‘I’ rather than ‘you’.

For example, instead of saying ‘You always talk about yourself. Why are you always so selfish?’, you could say ‘I’m feeling left out of our talk tonight and I need to vent. Can we please talk about my day?’.

If the Four Horsemen are ringing alarm bells for you, thankfully the experts say that there are easy ways to eliminate them in your relationship

The antidote to contempt, meanwhile, is building a culture of appreciation and respect.

For example, instead of rolling your eyes and saying ‘You forgot to load the dishwasher again? Ugh. You are so incredibly lazy,’ you could say ‘I understand that you’ve been busy lately, but could you please remember to load the dishwasher when I work late? I’d appreciate it.’

If it’s defensiveness that you struggle with, the Gottman Institute advises accepting responsibility.

So instead of saying ‘It’s not my fault that we’re going to be late. It’s your fault since you always get dressed at the last second,’ you could rephrase it as ‘I don’t like being late, but you’re right. We don’t always have to leave so early. I can be a little more flexible.’

Finally, if you recognise yourself stonewalling, experts say that you should take a break and soothing yourself during arguments.

‘When you take a break, it should last at least twenty minutes because it will take that long before your body physiologically calms down,’ the Gottman Institute explained.

‘Spend your time doing something soothing and distracting, like listening to music, reading, or exercising. It doesn’t really matter what you do, as long as it helps you to calm down.’