Manafort's lawyer suggested that the affair - which included a London pad, first-class plane trips and luxury hotels - cost up to $3 million.
Rick Gates is seen on the witness stand as a message between he and his former boss, Paul Manafort, appears before the court during Manafort's trial in Virginia. On Monday, he testified that he helped Manafort file false tax returns and hide his foreign bank accounts. Oh, and he says he did it all "at the direction of Mr. Manafort".
The questioning is part of the Manafort defense strategy of presenting Gates to the jury as someone who lies and can not be trusted.
Four employees at Dr. K's firm established and named the entities - Leviathan Ltd. and Peranova Ltd. are two of the more high-profile examples - where Manafort and Gates held millions of dollars of payments to Manafort's Davis Manafort Partners (DMP) and DMP International from their overseas political clients.
The vendors testified about how Manafort paid for his luxury goods, including cars and custom suits, by using direct wire transfers from accounts overseas.
Gates, who also worked on Trump's campaign, is the star witness against Manafort.
In another heated exchange, Downing tried to press Gates into explicitly saying that he had embezzled money from Manafort.
In a final back and forth between lawyers over Gates's credibility, the focus turned to his decision to plead guilty and cooperate with special counsel Robert Mueller's investigation, which Manafort's defence have portrayed as an attempt to save his own skin.
"I'm here to tell the truth and take responsibility for my actions", Gates said in response to a question from Downing about his trustworthiness.
The tax and bank fraud charges in the current trial - the first of two Manafort is scheduled to face - however, have nothing to do with Manafort's work on the Trump campaign.
Prosecutor Greg Andres pointed out that he had created a "loan forgiveness letter between Mr. Manafort and Mr. Manafort".More news: Saudi Arabia expels Canadian envoy, recalls its own over 'interference'
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During a series of redirect questions on Wednesday, Manafort's attorney Kevin Downing asked Gates if he remembers telling special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russian Federation probe MORE's office that he had four extramarital affairs.
Manafort was chairman of Donald Trump's presidential campaign, and his longtime deputy was part of the campaign, too.
In other testimony, Gates recounted how he falsified documents for Manafort, including converting a PDF of a profit-and-loss statement to a Microsoft Word document so he could doctor it to inflate the business' income.
Gates testified that he'd followed Manafort's instructions as they set up Cypriot and other foreign bank accounts, moved money from Ukrainians into the United States, made sure Manafort's name was scrubbed from the accounts, then lied to the IRS and banks.
The judge asked the lawyers to come to the bench to discuss the matter.
According to Gates, Manafort had a great deal of knowledge and control over the dispensation of funds-personally signing on the payments "hundreds" of times.
Jurors saw emails from Manafort imploring Gates to help a banker, Stephen Calk, make inroads into the campaign, inauguration and administration.
By that time, Gates was working on Trump's inaugural committee.
In October 2016, for instance, Gates sent Manafort DMP's profit and loss statement (P&L) from January 1 through June 30 of that year, emails introduced in court Tuesday show. He frequently used the phrases "It's possible" and "I don't recall" as Downing challenged him about inconsistencies in testimony he gave to the special counsel's office.
Gates told the court in Alexandria, Virginia, that he had met with government lawyer Greg Andres and Federal Bureau of Investigation agents 20 times and been told only to tell the truth, without any guarantee that he will be spared prison.