Clendenin was the spokesperson for the Highway Patrol for nine years.
In March, he was promoted to the rank of Major after 22 years with the department. In his new role, he oversaw the IT unit, and the logistics section that handles all the equipment troopers need on the road.
Reuben Young, Secretary of the Department of Crime Control and Public Safety, said at a news briefing Wednesday morning that the department began an investigation of Clendenin last week after getting allegations of inappropriate text messages.
"While this is an unfortunate occurrence, it is not reflective of the outstanding character and history of this great organization. We are committed to maintaining zero tolerance for inappropriate actions and will continue to work to keep the confidence and trust of the people of North Carolina," he said.
Young said the investigation was still ongoing and refused to give more details.
Clendenin's resignation came after another trooper resigned earlier this month amidst an investigation of alleged misconduct. That trooper was just the latest in a long line of officers being investigated for everything from inappropriate sex, to K-9 abuse, to drunk driving, and deadly accidents.
ABC11's I-Team did some checking, and in the last three years, the patrol has had to fire at least five troopers and has accepted at least six resignations.
Young said the public should not take its overall perception of the Highway Patrol from the actions of a few officers.
"It's unfortunate that we have people from time to time who make bad decisions, exercise poor judgment," said Young. "When they do that, we address those issues within the confines and the policies of the North Carolina State Highway Patrol. But we're going to keep working hard and we're going to keep studying what we need to do to try and improve upon making our troopers more prepared for what they do and more mindful of how they should conduct themselves out on the highways."
Still, Wednesday's announcement clearly irritated Governor Beverly Perdue.
"This is just a mark on the patrol. It's wrong. And everybody from Murphy to Manteo has to shape up and understand that zero tolerance is enforced in this administration," she said. "It's an absolutely unacceptable behavior. And I don't care if it started yesterday or 30-years ago. Zero tolerance is the guideline and the litmus test. And I mean it."
Clendenin himself released his own statement Wednesday saying in part, "I have used poor judgment concerning a matter. However I have not engaged in a sexual relationship with a co-worker. I have apologized to Colonel Glover for the embarrassment my actions have caused."