The House Intelligence Committee is preparing to hear Friday from former U.S. Ambassador to Ukraine Marie Yovanovitch , the third witness to publicly testify in the impeachment investigation into President Donald Trump .

Yovanovitchs hearing comes after diplomats Bill Taylor and George Kent publicly testified Wednesday for six hours about Trumps attempt to freeze U.S. military aid to Ukraine until the country agreed to publicly commit to investigating former Vice President Joe Biden , who is running for president.

Yovanovitch was removed in May as ambassador in Kyiv after Republicans complained that she was undermining efforts to pressure Ukraine to investigate Trumps political rivals. She privately testified Oct. 11 in the impeachment investigation, in which she said the president was politically motivated to pressure the State Department to remove her.

Here are five things to know before watching the Houses public impeachment hearing with Yovanovitch:

1. Why She Was Removed As Ambassador To Ukraine

Yovanovitch was abruptly removed from her post on May 6 despite being scheduled to end her stint there months later. The removal came after conservative media outlets and Donald Trump Jr. accused her of being part of an alleged Ukrainian attempt to support Hillary Clintons presidential campaign in the 2016 election, which she denied.

The veteran foreign service officer said her ouster happened after she insisted to Trumps personal attorney Rudy Giuliani that his requests for Ukraine to conduct certain investigations be relayed through the proper foreign policy channels. After Yovanovitch was removed, Giuliani announced that he would be traveling to Ukraine.

At the time of her ouster, Democrats slammed the decision as a political hit job. Yovanovitch is still employed by the State Department and currently holds a fellowship at Georgetown University.

Yovanovitch privately testified that Trump pressured the State Department to fire her as a concerted campaign against me because she refused to allow Giulianis shadow diplomacy.

She said she was incredulous that the U.S. government chose to remove an Ambassador based, as best as I can tell, on unfounded and false claims by people with clearly questionable motives.

She was replaced by Bill Taylor, the charg daffaires to Ukraine, who testified Wednesday about his concerns regarding Trump and Giulianis backchannel to the country.

Despite her being a nonpartisan career official, Republicans on the House Intelligence Committee will likely attempt to discredit Yovanovitch by bringing up the false rumors that led to her removal: that she was actively anti-Trump.

2. She Received Threatening Messages, Including From Trump

In Trumps infamous July 25 call with Ukrainian President Volodymyr Zelensky the call that helped fuel the impeachment inquiry the U.S. president threatened Yovanovitch by calling her bad news and ominously saying she was going to go through some things. Zelensky said he didnt support Yovanovitch because Trump told him she was a bad ambassador.

At her private hearing, Yovanovitch testified that she felt shocked and threatened by the presidents comments. She said a senior Ukrainian official warned her that I really needed to watch my back.

The summary of the Ukraine call suggested that Trump was angry at Yovanovitch on the basis of claims made by Ukraines former top prosecutor Yuriy Lutsenko.

Yovanovitch testified that Ukrainian officials told her at the end of last year that Giuliani was communicating with Lutsenko and that they had plans, and that they were going to, you know, do things, including to me. She added that Lutsenko was looking to hurt me in the U.S.

3. Rudy Giulianis Campaign To Oust Her Was Largely Fueled By Yuriy Lutsenko

Yovanovitch said that Giuliani went behind her back to try to replace her by meeting with former Ukrainian Prosecutor General Yuriy Lutsenko. Lutsenko was Giulianis initial point of contact in persuading Ukraine to investigate the Bidens after Yovanovitch refused to help him.

According to The New York Times , Lutsenko had a personal animus toward Yovanovitch while he was Ukraines prosecutor general because of her complaints that his office was filled with corrupt employees. She also reportedly told Lutsenko to stop investigating anti-corruption activists who were critical of his work and were supported by the American Embassy. Lutsenko snapped at Yovanovitch, telling her that no one is going to dictate to me who should be investigated, according to the Times.

Lutsenko falsely accused Yovanovitch of interfering with the 2016 elections by giving him a do not prosecute list and blocking Ukraine from giving evidence of corruption in the election to the U.S. He later admitted that he was the one who requested the list but still communicated the rumors to Trumps inner circle, eventually resulting in Yovanovitchs ouster.

Lutsenko was fired in August by Zelensky, and Ukrainian authorities said in October that theyre investigating him for allegedly abusing his power in dealings with politicians.

4. Giuliani Coordinated Her Removal With Lev Parnas and Igor Fruman

Yovanovitch privately testified that Giulianis business associates Lev Parnas and Igor Fruman coordinated with him in trying to replace her with someone more favorably inclined toward their business dealings in Ukraine.

Parnas and Fruman, Soviet-born Florida businessmen, allegedly set up the meetings between Giuliani and Lutsenko. They also managed to help build congressional support for removing Yovanovitch, including from Rep. Pete Sessions (R-Texas), who sent a letter urging Secretary of State Mike Pompeo to remove the ambassador because of allegations she was anti-Trump.

I didnt understand that because nobody at the embassy had ever met those two individuals, Yovanovitch testified of Parnas and Fruman. And you know, one of the biggest jobs of an American ambassador of the U.S. Embassy is to promote U.S. business. So of course, if legitimate business comes to us, you know thats what we do, we promote U.S. business.

She said Ukraines Interior Minister Arsen Avakov warned her that Giuliani had sought a meeting with him but he refused out of discomfort with the attorneys activities.

Yovanovitch alleged that Parnas and Fruman were looking to export liquid natural gas to Ukraine, which the embassy usually supports. But a Ukrainian official told her in February 2018 that Giuliani and the associates were also attempting a very dangerous move by looking into Ukraines involvement in the 2016 U.S. presidential election. That led the businessmen to consider her an obstacle in their reported scheme to purge the leadership of Naftogaz, Ukraines national oil and gas company.

Parnas and Fruman were recently indicted on charges of making campaign contributions to a Trump-aligned super PAC using straw donors last year.

Parnas said Nov. 4 that he was prepared to cooperate with the Houses subpoena after Trump openly denied knowing him at the time of his arrest. He also alleged Nov. 11 that he himself directly told Ukrainian officials that military aid was contingent on the Biden investigation.

5. Many Diplomats Were Angry At The State Departments Lack Of Support For Her

Secretary of State Mike Pompeo oversaw Yovanovitchs abrupt removal. Many of the diplomats who have testified said that they voiced concern over the fact that the State Department did not come to Yovanovitchs defense when she was disparaged and eventually removed from her post. Some of those witnesses included Deputy Assistant Secretary for European and Eurasian Affairs George Kent, who testified Wednesday, and Pompeos former senior adviser Michael McKinley.

Yovanovitch testified that she went to Pompeo to seek a reaffirming public statement of support after the barrage of negative press and the disparagement that she felt undermined her credibility. The State Department told her there was caution about any kind of statement, because it could be undermined by a Trump tweet.

David Hale, the third-ranking official at the State Department, testified to the House that the department believed publicly defending Yovanovitch would have hurt efforts to lift Trumps freeze on military aid to Ukraine and that senior officials were concerned about Giulianis reaction.

Yovanovitch also said Thomas Ulrich Brechbuhl, the State Departments counselor, was in charge of handling her removal but that he refused to meet with her when she came back to Washington.

McKinley testified to the House that he resigned partly due to the State Departments lack of support for Yovanovitch and the agencys increased politicization.