Billionaire investor and one of President Donald Trump's closest allies Tom Barrack will not be attending the Future Investment Initiative conference in Saudi Arabia, CNBC has learned.

Barrack will no longer be attending as his speaking session was cancelled by the conference hosts after Treasury Secretary Steven Mnuchin pulled out of attending on Thursday, according to a source with direct knowledge of the matter.

Mnuchin and Barrack were slated to be on a panel together next Tuesday in Riyadh.

Barrack is the latest prominent business figure who have dropped out of taking part in the conference, also known as "Davos in the Desert," following the disappearance of Washington Post columnist Jamal Khashoggi.

A spokesman for Barrack declined to comment.

Barrack, a Lebanese American, became close to the president and his operation during the 2016 presidential election. He was one of the lead business figures who helped raise funds for then-candidate Trump and later introduced him to his previous campaign chairman Paul Manafort. Barrack later served as chairman of Trump's inaugural committee

Barrack himself has strong business ties to the Middle East. He reportedly has $200 million invested into the region. His real estate investment firm, Colony Capital, manages at least $34 billion in assets, including $18 billion in over 16 commercial real estate and distressed debt-focused funds.