Longtime Oklahoma assistant Cale Gundy -- who's been helping coach the Sooners football team for over two decades -- has resigned ... after he says he uttered a "shameful and hurtful" word during a team meeting last week.

Gundy explained the situation in a lengthy statement on his social media page Sunday night -- saying he inadvertently used the word while reading off a player's iPad in a film session.

"I instructed my players to take notes," said the 50-year-old, who had just been tapped this offseason to coach the Sooners receivers this year. "I noticed a player was distracted and picked up his iPad and read aloud the words that were written on his screen. The words displayed had nothing to do with football."

He continued, "One particular word that I should never -- under any circumstance -- have uttered was displayed on that screen. In the moment, I did not even realize what I was reading and, as soon as I did, I was horrified."

Gundy did not say which word he used, but he did say it was "shameful and hurtful."

"The unfortunate reality is that someone in my position can cause harm without ever meaning to do so," Gundy said. "In that circumstance, a man of character accepts accountability. I take responsibility for my mistake. I apologize."

Gundy -- whose older brother, Mike Gundy, is Oklahoma State's famous head coach -- leaves his position with the Sooners after having coached the team in some capacity every year since 1999.

The former OU quarterback initially joined Bob Stoops' staff in '99 as a running backs coach. In the ensuing seasons, he held multiple different roles -- and had just been retained by new OU head coach Brent Venables this offseason.

"It's with sadness that I accept Coach Gundy's resignation," Venables said Sunday night. "He's dedicated more than half his life to Oklahoma Football and has served our program and university well."

"We're thankful for that commitment. We also acknowledge that in stepping aside he's placed the program and the welfare of our student-athletes first. In coaching and in life, we're all accountable for our actions and the resulting outcomes."

Ex-Sooners star Joe Mixon took to Twitter following the news and defended Gundy -- saying the coach "is not a racist in any way nor has a racist bone in his body, mind, or soul."

L'Damian Washington will now serve as the interim receivers coach.