Relations have been frosty between France’s Macron and Turkey’s Erdogan for years.
But a war of words over cartoons of the Prophet Mohammad has dragged them to an unprecedented low -
and it could have far-reaching consequences.
Let’s take a closer look at Franco-Turkish ties - and where the tensions could lead.
Last month a French teacher was beheaded for showing pupils cartoons of the Prophet.
The French government, backed by many citizens, saw it as an attack on freedom of speech.
Macron vowed to redouble efforts to stop radical Islam subverting French values.
"Our citizens today must be protected. Our citizens, whose religion is Islam, must be protected in our country, against these evils which is radical Islam."
That prompted Erdogan to accuse Macron of an anti-Islamic agenda -
even suggesting he needed a mental health check.
Western countries mocking Islam, he said, want to "relaunch the Crusades."
Both are facing domestic pressure on this issue: Macron, to be strong against radical Islam - and Erdogan, to be a global champion of Muslim rights.
But relations had already soured around other issues.
At their root? Rival strategic interests, according to analysts and officials.
Macron is the most outspoken defender of European interests in areas where Ankara – rebuffed for membership of the EU club – is increasingly exerting itself.
Namely - in north Africa, the eastern Mediterranean, and Syria.
In March 2018, Macron met a delegation including the Syrian Kurdish YPG - labeled a terror group by Turkey.
France accused Turkey of backing radical Islamists among rebels fighting President Bashar al-Assad.
France also claimed Turkey was using Syrian refugees as blackmail -
by hinting it could send them towards European borders.
Erdogan repeatedly threatened, in public speeches, to "open the gates."
By the time Erdogan and Macron met at a NATO summit in July 2018, relations were particularly low.
An official said everyone was sent out, apart from interpreters, so Erdogan and Macron could talk man to man.
But there was no thaw - if anything, there was a deterioration.
So - if bridges can’t be mended, where might it all lead?
EU leaders have already threatened sanctions if Turkey fails to de-escalate tensions in the eastern Mediterranean.
Sources say momentum is likely to build for a proposal, driven by France, to push through sanctions - targeting Turkey's already-fragile economy.