NATO leaders sought to make a show of unity on Wednesday as they met to conclude their annual summit, but the alliance's chief admitted a festering row with Turkey was still unresolved.
What should have been a celebration of NATO's 70th birthday has been overshadowed by bitter rows about money and the future strategy of the alliance.
Last year, the Western allies' get-together was derailed by US President Donald Trump's demand for greater European defence spending, but 2019's provocateur was France's Emmanuel Macron.
The French president has called for a renewed strategic dialogue with Moscow and demanded that Turkey explain itself over its assault -- backed by Syrian rebels Paris sees as extremists -- on Kurdish forces and its purchase of the Russian S-400 air defence system.
Turkish President Recep Tayyip Erdogan meanwhile has threatened to hold up NATO efforts to bolster the protection of the Baltic republics against Russia unless the allies brand the Kurdish militias who defeated the IS group in Syria as "terrorists".
Amid fears Erdogan could even veto the summit declaration and with barely two hours to go before the leaders sat down for their sole roundtable, NATO Secretary General Jens Stoltenberg admitted a solution to the row with Turkey had still not been found.
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"I'm confident that we will be able to find a solution to the issue related to the updating the revised defence plans," he said as he arrived for the summit at a luxury golf hotel in Watford, on the outskirts of London.
"I discussed this with President Erdogan last night and we are working on the issue as we speak." The summit host, British Prime Minister Boris Johnson, played down the dispute.
"There is far, far more that unites us than divides us, and I think one thing every leader here is absolutely resolved upon is the vital importance of NATO for our collective security," he said as he arrived.
The leaders met in various groups in London on Tuesday before having dinner with Queen Elizabeth II in Buckingham Palace, but Macron refused to withdraw his charge that NATO strategy is "brain dead" and Trump continued to insist some capitals were "delinquent" in paying their way.
The row set up a tense last day of what NATO had hoped would be a 70th anniversary show of unity for the "most successful military alliance in history", and a demonstration that the West can stand up to challenges from Russia and China.
Adding to the disjointed mood, the leaders of Britain, Canada, France and the Netherlands were caught on camera at the palace reception mocking Trump's lengthy media appearances.
After Macron's one-on-one pre-summit meeting with Trump had been preceded by a lengthy question and answer session with the media, Johnson was seen asking him: "Is that why you were late?"
Canada's Prime Minister Justin Trudeau interjects: "He was late because he takes a 40 minute press conference off the top."