Oklahoma Labor Commissioner Mark Costello died on Sunday after being fatally stabbed by his adult son in an Oklahoma City restaurant.

Officials say that Costello's 26-year-old son Christian used a steak knife to stab his father to death, after the two got into a heated argument at a Braum's ice cream and fast food restaurant around 6:30 p.m. Sunday evening, reports KOKH-TV. Officials added that the commissioner was stabbed at least four times and at least one time in the head.

"He made his way around the Braum's seeking help," Oklahoma City police Lt. Alex Edwards told Fox News. "He then went outside to the south of the restaurant and was confronted again."

Once police arrived on the scene, they found Costello, 59, sitting in a vehicle in the restaurant parking lot with several stab wounds. He was then taken to a hospital, where he was pronounced dead.

Meanwhile, Christian was arrested and charged with murder in the first degree, authorities said.

"Our hearts ache as an agency for this tragic event and our department grieves for his family during this very difficult time," said the Labor Department Chief of Staff Jim Marshall in a statement.

His biography states that Costello, a Republican who was elected as Oklahoma's labor commissioner in 2010, had a wife and five children.

"Mark Costello was a tremendous leader, colleague and most importantly friend to all of those at the Oklahoma Department of Labor," Marshall said in a statement posted on the department website.

During a news conference Monday morning, Oklahoma City Police Capt. Paco Balderrama told reporters that Mark and Christian had agreed to meet at the restaurant on Sunday to reconcile, after having an argument earlier that day, reports the Washington Post. However, their meeting turned violent.

"They were both there willingly, but as far as what set him off to attack the commissioner, we don't know," Balderrama said.

The attack spilled out into the parking lot as Mark tried to flee, police said. His wife also tried to intervene to stop the attack, but "she was unsuccessful," Balderrama said.

Witnesses, however, managed to subdue Christian in the parking lot until authorities arrived, Balderrama said.

The Costello family released a statement Monday, revealing that Christian suffered from mental illness.

"Our son, Christian Costello, has experienced many difficulties over the past several years," reads the statement. "Christian, like thousands of Oklahomans, struggles with a mental health disease and like many families we did our best to support him. Mark was committed to being there for his son and provided whatever help he could as a father."