Alexander Forbes non-executive director Moses Kgosana has resigned after being implicated in the Gupta emails.
He was due to take up the role of chairman on 31 August.
Questions have been raised about an audit of the Gupta wedding in 2013 after a clean audit was given by KPMG with Kgosana the South African CEO at the time.
KPMG has been accused of failing to raise the alarm after R30 million in public money was allegedly diverted to pay for the wedding.
The amaBhugane investigative unit says leaked Gupta emails show that R30 million was allocated by the Free State government for the wedding.
KPMG says it will investigate with emails showing that the family's companies categorised the funds used as business expenses, meaning they would not have to pay tax.
KPMG ended its dealing with the family two years ago, but prior to that, it did give the Gupta family a clean audit.
Then Kgosana says the firm did not know about the payments.
But questions were raised with emails showing that Kgosana wrote to Atul Gupta thanking him for being invited to the wedding, saying it was the event of the millennium.
Kgosana says he fears the allegations will interfere with his deliverable expectations at Alexander Forbes.