Brigitte Macron's infamous slap of her husband Emmanuel was sparked when she saw a message on his phone from an Iranian actress, a new book has claimed.

In the viral video from May last year, the first lady was seen pushing the French president in the face as the couple prepared to get off a plane in Vietnam.

At the time, Macron insisted the incident was 'nothing', and said he was just 'bickering, or rather joking, with my wife'.

But French journalist Florian Tardif has painted a rather different picture in his new book, '(A (Nearly) Perfect Couple)' - which promises to deliver an 'investigation' into the 'forbidden zones' of the husband and wife.

Speaking on RTL radio on Wednesday, Tardif - a journalist at Paris Match who has been following the Macrons since 2017 - called the notorious moment a classic 'couple's scene'.

'What happened is that she [Brigitte Macron], saw a message from a well-known figure. An Iranian actress,' he said.

Tardif claims that Macron maintained a 'platonic' relationship with the acclaimed star 'for a few months', but wrote her 'messages that went quite far', such as: 'I find you very pretty.'

'That's what I've been told by those close to him, and that's what I'm saying this morning,' Tardif said, insisting he has 'verified' the story and that everything in his book is based on 'facts'.  

These messages caused 'tension' within the couple, culminating in a heated and 'significant' argument aboard the presidential plane on the tarmac at Hanoi airport, the journalist claimed.

'This private scene became public because there was a misunderstanding on the plane. We thought the argument was over. It wasn't,' he concluded.

Tardif claimed the Elysee actually regretted not being honest about the dispute, 'simply because they could have shown at that moment that they were a couple, a real couple, not a perfect couple.'

At the time, an Elysee official described the episode as 'a moment when the president and his wife were relaxing one last time before the start of the trip by having a laugh'. 

Brigitte Macron's representatives denied to Le Parisien on Wednesday that the scene was linked to the Iranian actress and further emphasised that the First Lady would never check her husband's phone. 

'Brigitte Macron categorically denied this account directly to the author on March 5, specifying that she never looks at her husband's mobile phone,' the president's entourage said, adding that this detail had not been published by the author. 

In April, Donald Trump made a mocking reference to the infamous episode in a speech at the White House, provoking fierce condemnation across France.

'Then I call up France, Macron - whose wife treats him extremely badly - he's still recovering from the right to the jaw,' the US President joked at the White House Easter lunch, eliciting laughter from the audience.

Macron immediately responded, saying the comments about his marriage were 'neither elegant nor up to standard'. 

The joke sparked widespread anger among politicians across the country, including Macron's critics. 

Even Manuel Bompard, coordinator of the hard-left France Unbowed party, rushed to his defence.

'You are aware of the extent of my disagreements with the president, but for Donald Trump to speak to him like that and to speak of his wife in such a manner – I find that absolutely unacceptable,' Bompard told broadcaster BFMTV.

The 25-year age gap of France's first couple has long sparked spirited debate.

Brigitte, 73, first met Emmanuel, 48, when he was a 15-year-old in her drama class in a Catholic school in Amiens, northern France. 

She was 39, married, with a son and two daughters, the eldest of which shared a class with the future president.

In 'An (Almost) Perfect Couple', Tardif purports to revisit all the major decisions, turning points and controversies that have defined Macron's nine years in office.

In 2017, at the dawn of his first term, he claims Macron confided to a close friend: 'If Brigitte is unhappy, I won't be able to cope and I'll fail this five-year term.'