The advertising CEO at the center of an SEC investigation into his multi-million dollar expenses bill has just quit

Miles Nadal, the CEO of advertising agency holding group MDC Partners, and the executive at the center of a Securities and Exchange Commission investigation into his huge expenses bill, has stepped down from the company.

Nadal retired from his position as CEO and chairman of MDC - which owns agencies including 72andSunny and Crispin, Porter + Bogusky - on Monday, according to an SEC filing.

Nadal's expenses are currently subject to an SEC probe, which saw him promise to pay back the company $8.6 million in reimbursements because his expenses "lacked appropriate substantiation." MDC says in the SEC filing that the investigation, which has also seen the company set up its own special committee of directors to review its expense procedures, is still ongoing.

Nadal has also agreed to pay back an additional $1.8 million in relation to a separation agreement with the company, and a further $10.6 million in connection with amounts required to be repaid related to cash bonus awards. He is not eligible for compensation or severance payments, which would have reached some $27.2 million.

In June Nadal's perks package was ranked by Business Insider as the most extravagant in the advertising industry.

Nadal had received free travel from his residences in the Bahamas, and West Palm Beach, Florida to and from the company's corporate office in New York and to business events, totaling $91,038 in 2014. In addition last year, his pay package also included $71,967 for his personal use of a corporate apartment in New York City, and he was reimbursed $500,000 in unspecified expenses. The company also stumped up $263,000 in legal fees, which was in connection to the sale of 3.5 million MDC Class A shares and a secondary offering in 2014.

Nadal will be replaced by Scott Kauffman, who is currently the presiding director fo the board. The board of directors also appointed Irwin Simon, a current member of the board to replace Kauffman as presiding director.

The SEC filing also revealed that the company's chief accounting officer Michael Sabatino resigned on Monday. Sabatino has agreed to repay the company $208.525 in cash bonus payments received between 2012 and 2014, and he will not be paid any compensation or severance.

MDC Partners stock was down 6% at the time of writing.