Former President Trump said he had "automatic chemistry" with his running mate, Ohio Sen. JD Vance, in a Fox News interview on Monday.

Trump dismissed the pair's past disagreements as a misunderstanding before they got to know each other, saying Vance is now among his strongest allies.

"Originally, JD was probably not for me, but he didn’t know me," Trump said in the "Jesse Watters Primetime" interview. "And then when we got to know each other, he liked me maybe more than anybody liked me."

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President Donald Trump and his running mate J. D. Vance

Former President Trump and his running mate, Sen. JD Vance, speak with Fox News in an interview for "Jesse Watters Primetime." (Fox News)

The former president continued, "And he would stick up for me. And he’d fight for the worker as much as I fight for the worker. We just had an automatic chemistry."

Vance was an early critic of Trump in 2016, when the former president was campaigning to eventually beat Democratic presidential nominee Hillary Clinton

At the time, Vance had dismissed Trump as "cultural heroin" who was leading the disenfranchised working class into a "very dark place."

Private text messages leaked by Vance's former roommate show him calling Trump a "cynical" leader and wondering if he would be "America’s Hitler."

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JD Vance and his wife Usha Vance arrive the first day of the 2024 Republican National Convention at the Fiserv Forum in Milwaukee, Wisconsin

Republican vice presidential candidate Sen. JD Vance and his wife Usha Vance greet attendees during the first day of the 2024 Republican National Convention at the Fiserv Forum in Milwaukee. (Kamil Krzaczynski/AFP via Getty Images)

Vance's stance began to shift while Trump was in office, which the Ohio senator said proved many of his assumptions wrong.

Vance told Fox in 2021 that he would never deny having been anti-Trump going into his first administration but that he was happy to have been proven wrong.

"I’ve been very open that I did say those critical things and I regret them, and I regret being wrong about the guy," Vance said. "I think he was a good president, I think he made a lot of good decisions for people, and I think he took a lot of flak."

Trump endorsed Vance for the Senate in his successful 2022 campaign, further solidifying their alliance.

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Jesse Waters Donald Trump J. D. Vance

Former President Trump told Jesse Watters that he and Sen. JD Vance had "automatic chemistry" when meeting with possible running mates for his 2024 presidential campaign. (Fox News)

"I was wrong about him," Vance told CNN in May. "I didn’t think he was going to be a good president. And I was very, very proud to be proven wrong. It’s one of the reasons why I’m working so hard to get him elected."

In the recent interview with Watters, Trump offered specific praise for Vance's 2016 memoir, "Hillbilly Elegy," which shed light on the struggles of the White underclass in the U.S. – the world in which Vance grew up.

"It was all about the working men and women and how they aren’t being treated fairly. And he was right about that," Trump said. "And I understood that maybe better than anyone else. And we just have had a great relationship. And he had serious competition."