A professor at the center of the Russia investigation has disappeared from radar and has not responded to friends, colleagues, journalists, or even his fiancée for several months.

Joseph Mifsud, a professor from the Mediterranean island nation of Malta, met with former Trump campaign adviser George Papadopoulos in April 2016 and said the Russian government had emails that would be damaging to Democrat Hillary Clinton's presidential campaign. His name was made public last October and he has not been heard from since, according to BuzzFeed News.

The woman who was engaged to Mifsud told BuzzFeed she gave birth to a child he fathered earlier this year. Her repeated attempts to reach him, however, have gone unanswered.

The woman, identified as Anna, shared messages she and Mifsud exchanged with BuzzFeed to prove their relationship. She told him she was pregnant over the messaging app WhatsApp but he never came to see her at her home in Ukraine. At one point he claimed to be sick and suffering from heart problems, which he said prevented him from traveling.

Shortly after news broke of Papadopoulos' guilty plea for lying to the FBI as part of the Russia investigation, which is looking at whether the Trump campaign colluded with Russia, Mifsud went quiet.

It was reported earlier this year that Mifsud's bio was removed from one of the universities he worked at and he left his job at another school.

Anna said Mifsud told her he had a close relationship with Russian Foreign Minister Sergey Lavrov. He was also in Saudi Arabia and in Sicily at the same time President Donald Trump was last year.

The pair last saw each other in person last April, Anna told BuzzFeed.

The Trump campaign has denied colluding with Russia. The Department of Justice and multiple congressional committees are investigating that and also Russia's interference in the 2016 election. The DOJ recently announced the indictment of 13 Russians and three Russian companies for meddling in the election.