Donald Trump, Robert De Niro

And Donald Trump's latest Hollywood feud is with... Robert De Niro.

The real estate mogul fired back at the two-time Oscar winner Monday after De Niro criticized his birther obsession with President Barack Obama.

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"Well, he's not the brightest bulb on the planet," Trump said of De Niro during a phone interview on Fox & Friends. "I've been watching him over the years and I like his acting, but you know in terms of when I watch him doing interviews and various other things, we're not dealing with Albert Einstein."

Over the weekend, De Niro shared his thoughts about politics during an interview with Brian Williams at the Tribeca Film Festival. "I won't mention any of the certain people on the news in the last couple weeks," De Niro said. "But what are we doing? This is crazy. They're making statements about people that they don't even back up. Go get the facts before you start saying things about people."

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De Niro did not name Trump — who has been relentless in raising doubt over Obama's birth certificate — but answered in the affirmative when Williams asked, referring to Trump's Celebrity Apprentice: "Any of those people have shows on my network on Sunday night?"

"It's like a big hustle. It's like being a car salesman," De Niro said. "Don't go out there and say things unless you can back them up. How dare you? That's awful to do. To just go out and speak and say these terrible things? Unless you just wanna get over and get the job. It's crazy."

Trump countered Monday: "He can say what he wants, but the fact is that [Obama] has not revealed his birth certificate and a lot of people agree with me."

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De Niro is the latest celebrity to take a stand against Trump. Bill Cosby said last month that Trump was "full of it" when it came to his White House aspirations and last week, Jerry Seinfeld reportedly pulled out of a charity event in protest of Trump's questioning of Obama's citizenship.

Watch Trump call in to Fox & Friends: