In the latest brouhaha about race and the Trump campaign, Donald Trump Jr. answered questions during an interview from a controversial radio personality who believes that "slavery was the greatest thing to have ever happened" to African Americans. The younger Donald Trump says he had no idea that one of the radio hosts held that view.

"Had I known I would have obviously never done an interview with him," Trump told Bloomberg, adding that James Edwards, host of a radio programme called Political Cesspool, had not been vetted by his father's campaign staff.

Trump Jr. said that he was speaking to another radio host for a previously scheduled interview on the telephone when Edwards chimed in with questions. "He was brought into the interview without my knowledge," said Trump, 38, the executive vice president for the Trump Organization.

The incident follows concerns about his father's comments when the candidate was pressed on CNN about his position on an endorsement from David Duke, former grand wizard of America's most notorious white supremacist organization the Ku Klux Klan.

"Just so you understand, I don't know anything about David Duke. OK? I don't know anything about what you're even talking about with white supremacy or white supremacists," said the candidate.

Trump knew Duke well enough to call him a "Klansman" in 2000. He insisted he dodged denouncing Duke or the KKK on national TV because of a faulty CNN earpiece, though he clearly repeated Duke's name correctly.

He was also aware of Duke's endorsement days earlier when he was asked about it at a press conference. "I didn't even know he endorsed me. David Duke endorsed me?" Trump said before the CNN interview. "I disavow. OK?"

Trump Jr. said he has been grilled about Edwards' position to support the media's "false narrative that my father is racist."

"This is clearly the mainstream media trying to turn a story into something, much like they did with my father, who I witnessed denouncing David Duke and any KKK endorsement on multiple occasions," he added.