BRUSSELS -- U.S. President Donald Trump met his match in a handshake showdown with France's new president, Emmanuel Macron.

At their first meeting, ahead of a NATO summit in Brussels on Thursday, the two men locked hands for so long that knuckles started turning white.

Trump finally seemed ready to pull away -- but Macron evidently wasn't. The French leader held the shake for a few seconds more. Both men's jaws seemed to clench.

U.S. President Donald Trump (L) shakes hands with French President Emmanuel Macron before a working lunch ahead of a NATO Summit in Brussels, Belgium, on May 25, 2017. Reuters

Trump has described himself as "a germ freak" and called handshakes "barbaric." In his 1997 book "The Art of the Comeback," Trump wrote he'd "often thought of taking out a series of newspaper ads encouraging the abolishment of the handshake."

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Trump's aversion to hand-shaking seemed to lessen over the course of the U.S. presidential campaign. He's now deep into an inaugural world tour that has forced him to exchange hand greetings with leaders from Israel to the Vatican.

U.S. President Donald Trump (L) and France's President Emmanuel Macron shake hands before a working lunch ahead of a NATO Summit in Brussels, Belgium, on Thu., May 25, 2017. Reuters

Macron won France's election this month by positioning himself as the anti-Trump, embracing globalization and immigration.

But as a 39-year-old who has never held elected office, Macron clearly was excited about the appearance with the U.S. president, which cemented his status as a new global player -- and as a formidable hand-shaker.

Later, Mr. Trump extended his hand to Mr. Macron while the leaders gathered prior to the remarks at the unveiling of NATO's Article 5 and Berlin Wall memorials. The presidents shook hands momentarily before Mr. Trump quickly pulled back and they shared a laugh.