Washington (CNN) Energy Secretary Rick Perry is preparing for his exit from the Trump Cabinet with his name squarely in the middle of the Ukrainian controversy, raising the prospect that a once largely clean tenure could be clouded at the very end.

The controversy stems from a whistleblower's recent allegations that President Donald Trump asked Ukrainian President Volodymyr Zelensky earlier this year to investigate 2020 presidential candidate Joe Biden and his family, and that the White House attempted to cover up the conversation.

Perry was one of what one official called the "three amigos" leading US relations with the country, meeting at least three times with Zelensky.

In an interview with CBN News on Friday , Perry said, "as God is my witness," that neither Joe and Hunter Biden's name came up.

"I never heard, and I talked to the President about this, I had a conversation with - a phone call - with Rudy Guiliani about it. I've talked to the previous ambassador. I've talked to the current ambassador. I've talked to Kurt Volker, Gordan Sondland, the EU ambassador -- every name that you've seen out in the media and not once, not once as God as my witness, not once was a Biden name -- not the former vice president, not his son ever mentioned."

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