French President Emmanuel Macron joined in a singalong to a traditional chant during a night-time walk on the streets of Paris.
Footage surfaced of Mr Macron reading the lyrics to La Refuge from a phone as he sang with a group of young men.
The singalong came shortly after Mr Macron had addressed the nation on France's divisive pension reforms.
The Elysee Palace confirmed the video’s authenticity to French media, quelling suspicions that it was fake.
It was published online by the Canto Project, a publicly funded group that says its mission is to preserve the traditional songs of France.
The organisation said Mr Macron was “intercepted by a choir of friends rehearsing in the street” and agreed to take part.
The Canto Project has faced accusations of far-right leanings and publishing songs linked to Nazi Germany.
It denies the charge of extremism, saying last year that its repertoire includes both right and left-wing songs that have a place in history.
An aide to Mr Macron told AFP that the President, who was out walking with his wife Brigitte, could not have known “the backgrounds of every person he was speaking to”.
La Refuge is a song about a mountain lodge and is considered part of the catalogue of traditional music from the Pyrenees.
Mr Macron has sung La Refuge in public before. Last year, he joined in a chant in the Pyrenees during a stage of cycling’s Tour de France.
In his speech on Monday he promised 100 days of “appeasement, unity, ambition and action” after mass protests against his pension bill.
