Bill Taylor and George Kent, the first two witnesses in the House impeachment inquiry into President Donald Trump's dealings in Ukraine, testified for more than five hours Wednesday in a public hearing that saw both men share new — and sometimes shocking — pieces of information.

Taylor, the top U.S. diplomat in Ukraine, and Kent, a deputy assistant secretary of state who worked on Ukraine and five other countries, had testified last month, for hours, in a closed-door setting before the three committees leading the inquiry.

Here are five things we learned from their public appearance on Wednesday.

1. A new Trump phone call

In his opening statement, Taylor revealed that one of his staffers overheard a phone call between U.S. Ambassador to the European Union Gordon Sondland and President Donald Trump on July 26 — the day after the call between Trump and Ukrainian President Volodomyr Zelenskiy that prompted the impeachment inquiry.

The staffer heard Trump ask Sondland about "the investigations," Taylor testified, later clarifying to lawmakers that "investigations" meant probes desired by Trump and his personal attorney, Rudy Giuliani, into former Vice President Joe Biden and his son Hunter Biden as well as a conspiracy theory about the 2016 election.

Taylor testified that the staffer said Sondland told Trump that the Ukrainians were "ready to move forward" with those probes.

The staffer, Taylor testified, then asked Sondland what Trump thought about Ukraine. According to Taylor's account, Sondland said that "Trump cares more about the investigations of Biden."

The existence of this conversation was previously not known. Taylor said he'd only learned from the staffer about the call last week — weeks after Taylor had appeared before the committees behind closed doors.

2. Another potential witness

While Taylor did not, in his testimony, identify the staffer who overheard that Trump-Sondland conversation, two sources familiar with the matter told NBC News that the aide is David Holmes, the counselor for political affairs at the U.S. Embassy in Ukraine.

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As Wednesday's hearing got underway, two officials working on the impeachment inquiry told NBC News that Holmes will testify behind closed doors to the committees leading the inquiry on Friday.

3. Mulvaney part of 'irregular’ diplo channel

Taylor testified that White House acting chief of staff Mick Mulvaney was part of an "irregular" shadow communications channel between Washington and Kyiv that had sought a quid pro quo with Ukraine.

Taylor and others had previously testified that Giuliani was involved in a shadow diplomacy team that included Sondland; Kurt Volker, the then-U.S. special envoy to Ukraine; and Secretary of Energy Rick Perry. Kent, for his part, had previously testified that Volker, Sondland and Perry called themselves "the three amigos."

NBC News and other multiple other outlets have reported — and several officials have testified — that Mulvaney has played an integral role in the White House’s dealing with Ukraine, but Taylor citing him as a member of the "irregular" team is new.

4. Taylor took notes — lots of them

Taylor, responding to questions from the lawyer leading the questioning for the Democratic members of the Intelligence Committee, said he kept notes of all the conversations related to the White House's dealings in Ukraine that he'd mentioned in his opening statement.

Asked if he’d kept notes "related to most of the conversations, if not all of them, that you recited in your opening statement," Taylor replied that he had.

"All of them," he responded.

While Kent had testified last month that he took contemporaneous notes detailing some of his concerns, and while Taylor testified last month that he kept some "careful" notes, Taylor had not previously said that he kept such copious records of all the conversations mentioned in his testimony.

The notes kept by Taylor and Kent — which could prove vital to the inquiry — are the property of the State Department, which has not turned them over despite a subpoena from House Democrats.

5. A new way of saying 'quid pro quo'

At the center of the inquiry is the assertion by House Democrats that the Trump administration engaged in a quid pro quo with Ukraine when it conditioned U.S. military aid, as well as a White House meeting between Trump and Zelenskiy, on the Ukrainian government launching investigations into Burisma Holdings — the Ukrainian gas company that Hunter Biden joined as a board member in 2014.

Republicans, including the president, have denied that the White House engaged in a quid pro quo with Ukraine, with many saying that such a thing was impossible for reasons that include Ukraine not being aware that there had been a hold placed on the military aid.

Taylor testified Wednesday that, despite being told several times by Sondland that Trump was confident there was "no quid pro quo," Taylor strongly felt that wasn’t the case — and pointed to Sondland's use of the word "stalemate."

"Ambassador Sondland also said that he had talked to President Zelenskiy and Mr. Yermak [an aide] and had told them that, although this was not a quid pro quo, if President Zelenskiy did not 'clear things up' in public, we would be at a 'stalemate,'" Taylor testified. "I understood a 'stalemate' to mean that Ukraine would not receive the much-needed military assistance."