Rick Gates, the star witness in the federal case against ex-Trump campaign adviser Paul Manafort, on Tuesday acknowledged having an extramarital relationship in London while working for Manafort as the defense accused him of leading a “secret” and “second” life.

For the last two days in court, Gates has testified that he and Manafort committed bank and tax fraud together.

But during cross-examination on Tuesday, the defense painted Gates as living a “secret life” in London and accused him of embezzling money from Manafort’s foreign accounts at center of the trial to indulge in an extramarital affair in the United Kingdom.

“I’ve acknowledged there was a period where I had another relationship,” said Gates, who is married.

Gates' testimony also touched on an aspect of the Trump campaign. He described emails he received from Manafort about the chances that an economic adviser might be up for the post of Army secretary. Gates said the emails also asked for inauguration tichets for the adviser and his son.

In an aggressive cross-examination on Tuesday, Manafort’s lead attorney, Kevin Downing, said to Gates: “You stole from Mr. Manafort.”

Downing accused Gates of lying on expense reports to make trips to London and around Europe.

MANAFORT STARES DAGGERS AT RICK GATES, AS PARTNER-TURNED-WITNESS DETAILS BOOK-COOKING

Gates acknowledged during testimony on Monday to embezzling money from Manafort. But on Tuesday, he denied using that money to finance his extramarital relationship, saying he used “bonus money” and “family money.”

The questioning is part of the Manafort defense strategy of presenting Gates to the jury as someone who lies and cannot be trusted.

Downing summed up his questioning by asking Gates: "After all these lies, and the fraud you have committed, you expect this jury to believe you?"

"I am here to tell the truth and to take responsibility for my actions. Mr. Manafort had the same path,” Gates said. “I am here. I have accepted responsibility and I am trying to change.”

Under cross-examination, he admitted to paying off the full amount of his American Express balance with Manafort's money, including personal expenses, without his business partner’s knowledge.

During Gates’ testimony on Tuesday, Manafort stared coldly at Gates as the business partner-turned-witness testified against him. Manafort on Tuesday was seen with his arms folded, staring daggers as his former deputy testified as part of a plea deal. Manafort broke his stare only to review government exhibits on a small monitor in front of him.

Gates, who left the courtroom on Monday without so much as making eye contact with his ex-partner, looked only at the prosecutor during Tuesday's questioning.

Manafort is accused of committing tax and bank fraud with millions made through political work in Ukraine. He has pleaded not guilty to the charges.

Under questioning, Gates said when Manafort did consulting work for Ukrainian politicians, he would send the money he made to accounts in Cyprus. When they wired the money from Cyprus to the United States, Gates said, Manafort would list it as a "loan” to reduce his taxable income.

According to Gates, Manafort also reduced his taxable income by wiring money directly from those accounts in Cyprus to expensive vendors in the states for construction projects and fancy clothes.

Gates also testified that Manafort in 2014 expressed frustration to him about the amount he owed in taxes.

“Not happy. I just saw this. WTF,” Manafort wrote in an email to Gates, according to testimony, after learning accountants had added liabilities.

The trial is scheduled to continue Wednesday morning with Gates on the stand.

Fox News' Serafin Gomez, Jake Gibson and Paulina Dedaj contributed to this report.