Andrii Artemenko, a Ukrainian politician who sought to put a peace plan for the region in front of the Trump administration early last year, will testify in person in front of special counsel Robert Mueller’s grand jury Friday, Politico reported.

The politician told Politico he was subpoenaed last week and plans to comply.

Artemenko, the New York Times reported last year, was put in touch with Felix Sater — who for a time worked on various Trump business deals — through a mutual friend. Sater, in turn, introduced Artemenko to his longtime pal and President Trump’s personal attorney Michael Cohen. Cohen left a version of the proposal on the desk of then-National Security Advisor Mike Flynn, according to the Times.

Flynn was fired soon after and is now cooperating with Mueller’s probe, having pleaded guilty to lying to FBI agents about his Russian contacts.

Cohen has denied leaving the proposal for Flynn and has claimed to have thrown it out, according to Politico.

Artemenko’s proposal would have required a withdrawal of Russian forces from eastern Ukraine and would have allowed Ukraine to lease Crimea to Russia for a 50 or 100 year team, the Times reported. It would have also lift U.S. sanctions imposed on Russia by the Obama administration.

The revelation of Artemenko’s back-channel efforts was a major scandal in Ukraine, causing him to be ousted from his political party and making him the subject of a treason investigation, according to Politico. He was stripped of his Ukrainian citizenship in May 2017.