Outgoing adviser Omarosa Manigault Newman: 'Lack of diversity' at WH left her lonely, but Trump 'not a racist'

“It has been very, very challenging being the only African-American woman."

“It has been very, very challenging being the only African-American woman in the senior staff,” she told ABC News’ “Nightline” today.

Manigault Newman, communications director in the Office of Liaisons, said it “was very lonely” working alongside Trump’s other senior advisers – the majority of them white -- who “had never worked with minorities, didn't know how to interact with them.”

She added: “There was a lack of diversity that I will acknowledge.”

The White House announced Wednesday she will be leaving Jan. 20, after resigning to “pursue other opportunities.”

Her departure will leave the senior staff of Trump’s White House with no African-American representation, she noted.

When asked who will fill the void, Manigault Newman said, “That's a question that you'll have to ask President Trump and [Chief of Staff John] Kelly.”

“I regret that we haven't reached the level of diversity in this administration that I strove to see,” she said.

In response to Manigault Newman’s comments, White House Press Secretary Sarah Sanders today sought to defend the level of diversity within the West Wing, even though she couldn’t say how many African-American senior staffers are employed there.

“We have a really diverse team across the board at the White House,” she said at today’s press briefing. “We want to always continue to grow the diversity here. We're going to continue to do that.”

The White House did not immediately respond to ABC News' request for specific numbers.

Manigault Newman had been bothered by the president's highly controversial reaction to the white nationalist rally in Charlottesville, Virginia, in August that left one counterprotester dead, according to a source with knowledge of her thinking.

Trump was criticized for initially failing to condemn white supremacists and for doubling down three days later that there was “blame on both sides” and there were “some very fine people on both sides.”

“Yes, I will acknowledge many of the exchanges, particularly in the last six months, have been racially charged,” she said. “Do we then just stop and label him as a racist? No.”

“[Trump] was sad to learn about my departure,” she said, adding, “I regret that he found out about it on the television.”

ABC News' Jordyn Phelps and Alex Mallin contributed to this report.