David Holmes, the aide who overheard a phone call between U.S. Ambassador to the EU Gordon Sondland and President Trump, is testifying in a closed hearing with the House committees conducting the impeachment inquiry. Bill Taylor, the top U.S. diplomat in Ukraine, testified in an open hearing before the House Intelligence Committee Wednesday that Holmes, who he only identified as a member of his staff, had informed him of the July 26 call last week.

David Holmes, a State Department official, arrives to appear in a closed-door deposition hearing as part of the impeachment inquiry at the US Capitol in Washington, D.C., on November 15, 2019. OLIVIER DOULIERY / Getty

Holmes is a counselor for political affairs at the U.S. embassy in Kiev, according to the embassy's website.

According to a portion of Holmes' opening statement obtained by CBS News, Holmes said he and two unnamed staffers were at lunch with Sondland in Ukraine when Sondland called Mr. Trump. Holmes said that Sondland told Mr. Trump that the Ukrainian president "loves your ass."

"I then heard President Trump ask, 'So, he's going to do the investigation?' Ambassador Sondland replied that 'he's gonna do it,' adding that President Zelensky will do 'anything you ask him to,'" Holmes said, according to the statement.

Get Breaking News Delivered to Your Inbox

A source attending the closed hearing told CBS News that the deposition of Holmes was "very damning" for Sondland. The source said that Sondland will "either go to jail or have to turn on the president."

At the first public hearings of the impeachment inquiry, Taylor testified that a member of his staff, whom he did not name, was with Sondland at a restaurant on July 26 when the ambassador placed a call to Mr. Trump.

"The member of my staff could hear President Trump on the phone, asking Ambassador Sondland about 'the investigations,'" Taylor, the chargé d'affaires at the U.S. embassy in Kiev, said in his opening statement. "Ambassador Sondland told President Trump that the Ukrainians were ready to move forward."

Taylor said that the staff member, now known to be Holmes, asked Sondland after the call what the president "thought about Ukraine."

"Ambassador Sondland responded that President Trump cares more about the investigations of Biden, which Giuliani was pressing for," Taylor said. He told the Intelligence Committee that he was not aware of the conversation at the time of his deposition in October.

Democratic Congressman Ted Lieu told reporters that Holmes' testimony confirmed Taylor's story.

"He has firsthand knowledge of the conversation between Ambassador Sondland and the President of the United States. He overheard the conversation," Lieu said. Lieu added that Holmes "has some pretty specific quotes from that phone call."

Republicans have questioned why Holmes did not come forward with information about the July 26 call earlier. However, Democratic Congressman Jamie Raskin said Friday afternoon, "It's not later — we're in the middle of an investigation now."

"That's how investigations work. People come forward with information along the way. Remember, we haven't even drafted articles of impeachment yet, much less voted on them, much less sent it over to the Senate where the real trial takes place. So there's nothing remotely late about his coming forward," Raskin told CBS News.

Holmes' testimony comes directly after lawmakers on the House Intelligence Committee heard from former U.S. Ambassador to Ukraine Marie Yovanovitch in the second public hearing of the impeachment inquiry.

Yovanovitch, who was removed from her post in Ukraine in early May, testified that she was the victim of a smear campaign led by Rudy Giuliani and "foreign corrupt interests" in Ukraine, one that left her reputation tarnished after a career of public service that has spanned over three decades.

Margaret Brennan and Stefan Becket contributed to this report