French President François Hollande is urging Democrats in the US to "get Hillary Clinton elected," and says that a Donald Trump presidency could "complicate relations" between Europe and Washington. And he has a warning for the world: the Brexit referendum won unexpectedly, and that means Trump can too.

"Those who claim that Donald Trump cannot be the next president of the United States are the same who claimed that Brexit would never be voted in," Hollande said in aninterview with French daily Les Échos.

Hollande was candid about the presumptive Republican nominee, something that happens very rarely in international politics. It just isn't done that a democratic head of state or government expresses a political view on another democracy's upcoming election. But Trump is unusual.

Hollande, a Socialist, likened his policies to the fear-mongering tactics of far-right movements in the EU.

"His slogans are not that different from [those of] the far right in Europe and in France: fear of the wave of immigration, stigmatization of Islam, questioning of representative democracy [...]," said Hollande. The president also mocked Trump's hypocrisy when "denouncing the elites," describing the real estate mogul as "the most obvious incarnation" of those elites.

When asked by the interviewer if a Trump presidency could be "dangerous," Hollande answered in the affirmative, and said that Trump's election could make US-EU relations thorny. "The best thing that Democrats can do is to get Hillary Clinton elected," he said.

Hollande also warned against any complacency ahead of the 2016 US presidential elections, drawing a parallel with the June 23 referendum that resulted in a majority of UK voters choosing to leave the EU. The result of the Brexit vote shocked many in Europe and in the UK — including some voters who appeared to struggle with buyer's remorse in the cold light of day.

Bernie Sanders made a similar parallel in an opinion piece in The Times, likening Trump's policies to the message of those backing the "Leave" movement. "We do not need change based on the demagogy, bigotry and anti-immigrant sentiment that punctuated so much of the Leave campaign's rhetoric — and is central to Donald J. Trump's message," he wrote.

The latest polls show Clinton and Trump almost neck and neck in the race, with an estimated 42 percent of the vote for Clinton, and 40 for Trump.

While this is the first time the French president speaks out against Trump, France's prime minister took his gloves off in May, when he called the Republican candidate "a bad man."

The French are not the only ones to mince their words when it comes to the prospect of President Trump. In early March, German Economy Minister Sigmar Gabriel called Trump "a threat to peace and social cohesion, but also to economic development." Outgoing UK Prime Minister David Cameron — who announced he would step down following the referendum — once labeled Trump's plans to ban Muslims from entering the US as "divisive, stupid and wrong."