STILLWATER, Okla. -- Over the summer, Mike Gundy's youngest son noticed that his dad's hair had grown a little long at the back. Gage joked how funny it would be if his dad let his hair grow the way it flowed in college.

Gage didn't realize what he had started.

Soon he'd learn he wouldn't be able to stop it.

"I said to him, 'If you keep bothering me, I'm not going to cut it.'" Mike Gundy said. "Now I'm kind of enjoying it."

This season, Oklahoma State's country-hearted coach has turned the joke on his three sons, keeping the biggest, baddest hairstyle in all of college football.

The Gundy Mullet has galvanized his team and garnered approval from mullet royalty in the form of country music star Billy Ray Cyrus, who told ESPN.com that he'll be pulling for the Cowboys this weekend in Bedlam as a result.

"Coach Gundy rockin' the mullet? Yeah, shows class -- and brass!" said Cyrus, who once wrote homage to mullets. "More importantly, he's a great coach. He has inspired me. The team inspires me. I hope they run the table."

Mike Gundy debuted his mullet, albeit quietly, at Big 12 media days. Kevin Jairaj/USA TODAY Sports

Oklahoma coach Bob Stoops conceded that The Gundy Mullet has won him over, too.

"Heck, it's growing on me through the year, through the season," Stoops said. "Maybe wasn't such a fan early on.

"But I've come to like it."

Stoops isn't alone.

The Cowboys say The Gundy Mullet has played a role in their seven-game winning streak heading into the showdown at Oklahoma that will decide the Big 12 title.

According to quarterback Mason Rudolph, the mullet has provided the Pokes with "mojo." Safety Jordan Sterns says it has given the team "swag."

"I just love looking at it every day," said Oklahoma State defensive coordinator Glenn Spencer. "It's one of the highlights of my day to see where it's coming down his neck and touching his collar and now it's below the collar. You come in the office every day and you check it out, see what's happening with it.

"The wind will catch ahold of it and it'll look like a kite with a tail every now and then."

"Coach Gundy rockin' the mullet? Yeah, shows class -- and brass!"

Even Sooners quarterback Baker Mayfield copped to its prowess.

"It's ferocious," Mayfield said. "It's very dirty. You've got to respect that he's rocking it."

Gundy has rocked the mullet before, while quarterbacking the Cowboys in the 1980s, but its triumphant return caught those around him by surprise.

"The first time I discovered it was on the flight to media day," Rudolph said. "I was like, 'Has he not gotten a haircut? Or is he actually trying to do it?'"

Turned out, he was doing it.

During Big 12 media days, The Gundy Mullet quickly turned into the most talked-about storyline. As a mullet aficionado, Gundy attempted to explain that his wasn't a true mullet yet. "A real mullet has to be at least shoulder length," he said then. "And you've got to have some curls in it."

That did little to quell the buzz.

"[Linebacker Chad Whitener] took a picture of it on Snapchat during media days and said 'Gundy Mullet,'" said Oklahoma State tight end Zac Veatch. "So I thought, 'Well, maybe he hasn't gotten a haircut in a while. Maybe his wife was out of town.' That was the last I saw of it all summer.

"Then he comes in for preseason camp and I'm thinking, 'That's a mullet. That's a full-blown mullet. That's not a mistake. That's mullet.'"

Before long, mullet fandom took hold in Stillwater like a prairie wildfire. Oklahoma State's official apparel store even began offering mullet-branded merchandise.

What a world. You can now buy Mike Gundy mullet shirts from the #OKstate online store (https://t.co/zYMlarz13Q) pic.twitter.com/GKjhc1odjy — Kyle Fredrickson (@kylefredrickson) September 8, 2016

"He's got the perfect hair for it, too," Veatch said. "Goes up in the front, long at the back. I like him better with it."

Gavin, Gundy's oldest son who is a sophomore at the University of Arkansas, didn't realize his dad was actually going through with the mullet. That was, until he saw him on TV at Big 12 media days.

Mullet game too strong pic.twitter.com/3qzxqCeDUO — Gavin Gundy (@GundyChild) July 18, 2016

"At that point, I realized this was a thing and he was going to continue it," Gavin said. "I called him after and said, 'What is up with that hair?' He said Gage had told him to. He was bored and thought, 'Why not?'

"I knew then he was going to go for it."

Gage, however, has since reversed course, and has been pleading with his dad to cut his hair. Gundy finally made a deal with him earlier this month. If Gage got a 91 on a math test, he'd cut it.

To Gage's dismay, he got an 88.

Mayfield said that when he learned of this he became even more captivated.

"I heard from our Coach Gundy [Oklahoma offensive assistant, Mike's brother Cale] that he stuck with it because one of his kids said it was awful," Mayfield said. "You've got to respect that he's just doing it out of spite."

Gavin said his friends have become obsessed, as well.

"They think it's the 'frattiest' thing they've ever seen," he said. "They love to mess with me. They always send me pictures of it. When [Mike Gundy] came down for dad's day, he thought [showing off the mullet] was one of the funniest things he'd ever seen in his life.

"People don't know. They really only see the TV part of him, but he's one of the goofiest people you'll ever meet. He loves messing with us, trying to embarrass us."

That included pulling pranks on Gavin whenever he'd have friends over in high school.

"He loves doing that stuff," Gavin said. "That's why he's grown out the mullet -- that and he knows the players enjoy it. They like when he does stuff like that. He could care less what he looks like. He just loves having fun with his players."

Over Thanksgiving, Gavin said the Gundy family took turns volleying one-liners at his father about the mullet. The best ones, however, came from Grandma Gundy.

Gundy's current hair is reminiscent of his late-'80s glory days as a player at Oklahoma State. Gundy family

"Every time she turned and looked at it, she couldn't stop laughing," Gavin said of his grandmother, Gundy's mom. "She says it's like a time warp back to his college days."

Gavin thought for sure by now his mother would have forced Gundy to cut it. He was wrong.

"Seriously, I figured she'd think he was a dork for doing it," Gavin said. "I don't know if it's a throwback to the past or what, but I asked her, and she says she likes it."

The same goes for the Cowboy players, who swear the mullet has soothing powers.

"It puts a smile on our faces, eases our stress, relaxes us," said tight end Blake Jarwin. "I like him more with it. I think he needs to keep it from now on and make it his little tradition.

"Coach Gundy, when he does stuff like that, that's just who he is. It's part of his character. That's why people come play for him."

Meanwhile, this week for the first time, Gundy publicly said that he'd officially grown a mullet. It was a realization that arrived after deer hunting over Thanksgiving break.

"I hadn't washed my hair in like three days. ... I noticed it looked a little different," Gundy said. "It's not really curly, but it is a mullet now. It has definitely hit the mullet stage. The next step is, at some point I'm going to have to decide what to do with it. Because, obviously, it can't keep growing forever.

"Well, I guess it can. But next thing, I'll be singing 'Always On My Mind.'"

Cyrus has a more fitting suggestion.

"If it means a championship, I think 'I Want My Mullet Back,' too!" he said. "I just never thought I'd have to go to Oklahoma to get it."