During a press conference with Turkish President Recep Tayyip Erdogan on Wednesday, President Trump said he knows nothing about an alleged July 26 phone call with EU Ambassador Gordon Sondland in which he is reported to have asked about the status of Ukrainian investigations he sought into the Bidens and the 2016 election.

"I know nothing about that. First time I've heard it. The one thing I've seen that Sondland said is that he did speak with me with for a brief moment and I said "no quid pro quo under any circumstances." And that's true. But I've never heard this. In any event, it is more secondhand information, but I've never heard it."

— President Trump

Why it matters: In the first public impeachment hearing on Wednesday, acting U.S. Ambassador to Ukraine Bill Taylor revealed that he had been informed of the new revelation by a staff member last Friday.

The staff member, which has since been confirmed to be David Holmes, told Taylor that he overheard Trump discuss "the investigations" in Ukraine with Sondland the day after Trump's July 25 call with Ukrainian President Volodymyr Zelensky.

Sondland later told Holmes that Trump cared more about "the investigations of Biden" than Ukraine itself, according to Taylor.

Holmes has been called by House investigators to testify behind closed doors on Friday.

The big picture: The new detail suggests that Trump was more personally involved in Sondland and other U.S. officials' efforts to get Ukraine to announce these investigations, which have been condemned by Democrats and many of the impeachment witnesses as political.

Go deeper: Highlights from the impeachment hearing