Tony Gupta was a business partner as well as a "dear" and "close" friend of his, Duduzane Zuma told Deputy Chief Justice Raymond Zondo on Monday.
Zuma, the son of former president Jacob Zuma, was testifying at the state capture commission of inquiry in Johannesburg.
"I spent a lot of time with him on a daily basis," he said.
When Zondo asked him if Gupta was particularly close to him, he responded: "More than particularly close. That's my guy."
The latter part of the statement caused advocate Phillip Mokoena, part of the commission's team of evidence leaders, to chuckle.
Zuma confirmed in a letter in September last year - through his lawyers - that he was ready to testify in relation to a statement submitted to the commission by former deputy finance minister Mcebisi Jonas.
The inquiry will continue at 10:00 on Tuesday.
Watch the proceedings live on News24.