A former top aide to President Trump on European and Russian affairs has arrived on Capitol Hill to testify before Congress, where she is expected to detail a “shadow foreign policy” pursued by Trump’s personal lawyer Rudy Giuliani and U.S. Ambassador to the European Union Gordon Sondland.

Fiona Hill, a former special assistant to the president, on Monday is set to testify that Sondland and Giuliani went around the National Security Council and official White House protocol to speak directly with Trump about Ukraine, NBC reported last week.

Hill’s attorney, Lee Wolosky, confirmed that his client had received a subpoena and intended to answer questioning from members beginning at 10 a.m. She is the first former White House official to agree to cooperate with the House’s impeachment inquiry.