George Calombaris has apologised after a review revealed his restaurant group had been underpaying over 100 of their staff by a total of $2.6 million.

Of the 430 current staff working across the celebrity chef’s restaurants, 162 were underpaid over the past six years, which the celebrity chef attributed to “historically poor processes”, leaving him “devastated”.

“You, our amazing team, are the key to our success. I am so sorry we have messed up and let you down on a fundamental issue,” Calombaris said in an email to staff on Monday.

“I am devastated by what has happened and we have been working extremely hard to fix this. I want to be clear that getting it right means ensuring that every single one of our team members is paid what they are entitled to under the industry award, and that any outstanding money owed to staff is rectified.”

To rectify the matter, affected employees will be back-paid an average of just over $16,000 each.

Issues with the payroll were brought to the MAdE Establishment Group’s attention by Fair Work Ombudsman over 18 months ago, yet was not thoroughly investigated until October last year when Troy McDonagh was appointed as the new chief executive.

It was then that the company enlisted KPMG to conduct a comprehensive review into the issue.

“Regrettably, our attention to detail at that time wasn’t at a level it should have been, but we now have a CEO and human resources manager in place,” Calombaris said.

The mismanagement also saw nearly half of all staff members being overpaid their base salary, however an email to staff confirmed that they would “not be asked to pay back any money” and that they “will retain the same payments they are now on.”

The employees known to be affected worked at The Press Club, Gazi and Hellenic Republic, while those of souvlaki bar Jimmy Grants were not impacted, confirmed management.

The already significant payout figure is expected to increase as MAdE Establishment Group sets out to contact former staff.