Boris Johnson dismissed Emmanuel Macron as "Putin's lickspittle" after the French president criticised the then-prime minister's response to the Ukrainian refugee crisis, according to a former leading No 10 official.
Mr Johnson also called Mr Macron a "four-letter word that begins with c", former Downing Street director of communication Guto Harri said in his podcast Unprecedented.
"When the British press was giving the British Government a hard time over our response to the refugee crisis, Macron turbocharged it by criticising Boris pretty directly and his words were all over the front page of The Guardian," he recalled.
"Much as Boris is not prone to getting really cross, nor using particularly strong language, this was one where he really flipped at our morning meeting.
"He just launched into a violent attack on Emmanuel Macron. Basically, saying 'He's a four-letter word that begins with C, he's a weirdo, he's Putin's lickspittle . We need an orgy of frog bashing. I'm going to have to punch his lights out'."
Mr Harri said the two leaders had patched up their differences before a G7 summit a few weeks later.
The second episode of Unprecedented on Global Player also recounts Mr Johnson's relationship with Ukrainian President Volodymyr Zelensky, saying the two leaders "shared gallows humour" and recalling a phone call on the night Ukraine was invaded.
"It was massively sobering," said Mr Harri. "We really could not believe that this was seriously underway. A superpower advancing on a neighbour who had done nothing to provoke it.
"Boris could not have been clearer that we were there to help the Ukraine in whichever way we possibly could, using whatever we could possibly deploy within reason.
"The two of them had this extraordinary bond. And, dare I mention it, this kind of really dark gallows humour that was obviously a coping mechanism."
Listen to the second episode of Unprecedented on Global Player now.
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