Trump's billionaire friend Tom Barrack reportedly called his ties to the former president 'disastrous' for his business

• Former Trump advisor Tom Barrack is charged with illegal lobbying on behalf of the UAE.
• In testimony on Monday, the billionaire reportedly said Trump was "disastrous" for his business.

Donald Trump's billionaire friend Tom Barrack said Monday that his ties to the former president were "disastrous" for his business dealings, multiple outlets reported.

Barrack, who informally advised the former president during his 2016 campaign, made the comment on the stand at his own criminal trial in federal court in Brooklyn, New York, The Daily Beast reported.

The billionaire has been charged with illegally lobbying the Trump administration on behalf of the United Arab Emirates between 2016 and 2018. He also faces other charges including obstruction of justice and lying to the FBI.

He said his long-time relationship with Trump ended up being "disastrous" for him professionally and that business would be "unquestionably" better if he didn't support him in the 2016 presidential election, per The Daily Beast.

Barrack, who is the founder and former executive chairman of the investment-management firm Colony Capital, testified that Trump's political scandals made it harder for his company to keep its business with countries in the Middle East.

Barrack was charged in July of last year and his trial began earlier this month. He has pleaded not guilty and is expected to continue testifying on Tuesday.

Trump and Barrack became friends in the 1980s, and were described by journalist Michael Wolff as a "set of nightlife musketeers" in his 2018 book "Fire and Fury: Inside the Trump White House."

Barrack, was also a chair on Trump's inaugural celebrations, told the court he was supportive of Trump when he decided to run for president and began to advise him early on in his presidential campaign, CBS News reported.

"I thought this is an amazing thing in America that you can take a well-meaning entrepreneur person like Donald Trump and enter the fray, and it's a good thing for the system," Barrack said in court, per CBS News.

It is unclear if the two remain friends, though they have spoken at least once since the trial started last month, a source familiar with the matter told CBS News.

There is no evidence that Trump was aware of Barrack's alleged wrongdoing during his presidency.

A day before the testimony, Trump took to Truth Social to support Barrack, calling him a "highly respected businessman" who is "being unfairly persecuted."

"Our seriously Weaponized 'Justice' Department, however, has accused him of being a foreign agent of the UAE, which I do not believe he was," Trump added.

A representative of Trump did not immediately respond to Insider's request for comment.