PITTSBURGH — A Knoch High School graduate is at the center of the case in which Highmark’s CEO is charged with simple assault and defiant trespass.

The charges relate to a fight Highmark CEO Kenneth Melani had with Mark Myler, the husband of Melissa Lazar Myler with whom Melani was having an affair.

Melissa Lazar Myler is a 2002 Knoch graduate and a Slippery Rock University graduate. She had been the operations manager of the Mylan Classic, which was a Nationwide Golf Tour event in September 2010.

Melani, 58, was charged Wednesday by police in Oakmont in Allegheny County.

He showed up Sunday afternoon at the home of Mark Myler where the altercation occurred.

Melissa Myler told officers she had been having an affair with Melani since shortly after he hired her in October to work at Highmark.

In January, according to a criminal complaint, Melani’s wife discovered the affair and told Mark Myler. That prompted Melissa Myler to move out of their home in Oakmont and move in with Melani, the complaint says.

Highmark spokesman Michael Weinstein said in a statement that the situation is a personal matter and that Melani is taking an unpaid leave from the company, which is based in Pittsburgh and is an independent licensee of Blue Cross and Blue Shield Association.

Melani’s attorney, Robert Del Greco, did not immediately return a call seeking comment Thursday.

A woman who answered the phone at Melani’s home in Cheswick said he was not home and hung up.

Highmark chairman J. Robert Baum will serve as acting chief executive officer, said the company, which provides insurance to more than 4.8 million members in Pennsylvania and West Virginia and had a revenue of $14.6 billion in 2010.