Donald Trump, Jr. (R) greets his father Republican presidential nominee Donald Trump during the town hall debate at Washington University on October 9, 2016 in St Louis, Missouri. Getty Images

U.S. President Donald Trump's former attorney asserts that Trump knew in advance about a 2016 meeting between his campaign staff and Russians who claimed to have compromising information on Hillary Clinton, according to NBC News. Citing a knowledgeable source, NBC reported that the attorney, Michael Cohen, says that President Trump was told ahead of time about the meeting by his son, Donald Trump Jr. Cohen is willing to make that assertion to special counsel Robert Mueller, NBC said. Mueller is investigating whether the Trump campaign colluded with the Kremlin during the U.S. presidential election. U.S. intelligence services are in broad agreement that Russia directly interfered with the election.

President Trump's current attorney, Rudy Giuliani, told NBC that "Michael Cohen is not credible." "Michael Cohen can't be believed unless it's corroborated five times," Giuliani said. "I talked to the president about this at length before as well as other witnesses and it's not true. Why would you expect it would be true from someone like Cohen? A lawyer who would tape their own client is a lawyer without any character." The White House did not immediately respond to a CNBC request for comment.

Pre-election meeting to get dirt on Clinton

Donald Trump Jr. has repeatedly denied that he told his father in advance about the 2016 Trump Tower meeting. Trump Jr. agreed to the meeting at Trump Tower so that he could explore a Russian offer of supposedly damaging information on Democratic presidential candidate Clinton. His brother-in-law, Jared Kushner, and then-campaign manager Paul Manafort also attended that meeting in early June 2016.

Manafort is scheduled to go on trial next week on bank fraud and tax charges related to his work for a pro-Russia political party in Ukraine. Mueller is prosecuting that case. Thursday night's news broke hours after the Wall Street Journal reported that the chief financial officer of the Trump Organization, Allen Weisselberg, has been subpoenaed by a federal grand jury investigating Cohen for possible crimes.

Cohen attorney says revelation 'was not from us'