The House impeachment inquiry dismissed as “illegitimate” by the White House is about to hear testimony from a former top aide ready to go on the record about Trump attorney Rudy Giuliani’s “shadow policy” in Ukraine—along with the former ambassador to Ukraine who was reportedly ousted for refusing to put up with all the off-the-books maneuvering.

The Associated Press reports former U.S. ambassador to Ukraine, Marie Yovanovitch, was dismissed from her post after calling out Giuliani’s back-channel methods in his crusade to have Ukrainian authorities investigate debunked corruption allegations against one of Trump’s top political rivals in 2020, former Vice President Joe Biden.

A former diplomat said Yovanovitch made clear there were formal procedures to follow when requesting a country's help in an investigation, and recalled that she refused to participate in “offline, personal, informal stuff.”

After Yovanovitch was abruptly dismissed from her post earlier than expected in May as Giuliani pursued the investigations, national security officials reportedly raised concerns about her ouster and the lawyer's push to make it happen.

Additionally, Trump's former top aide to Russia and Europe will reportedly testify to Congress that Giuliani—along with U.S. Ambassador to the European Union Gordon Sondland—circumvented the National Security Council to pursue their own Ukraine “shadow policy.”

According to NBC News, Fiona Hill plans to tell lawmakers that Giuliani and Sondland bypassed former National Security Adviser John Bolton and other processes to access the president on Ukraine-related issues.

National security officials also raised concerns about Sondland. According to The Washington Post, he claimed Trump put him in charge of Ukraine relations and expressed in a meeting how Ukraine's corruption investigations “need to be started up again”—which officials understood to be a reference to the Biden probes.

Yovanovitch is scheduled to appear before the House Intelligence, Foreign Affairs, and Oversight Committees on Friday behind closed doors. Hill is also expected to testify before Congress on Oct. 14.