BYU will have a new defensive coordinator when it joins the Big 12 next year.

In a move that was not unexpected, seven-year BYU defensive coordinator Ilaisa Tuiaki announced via Facebook and Instagram on Sunday that he is stepping away from the program, after having been demoted from DC to defensive line coach last month.

“What a great 7 year run it’s been,” Tuiaki wrote. “It’s time to venture out and pursue a new challenge. I want to say thank you.”

He did not specify his next step, or even if he will remain in coaching.

“This job can’t sever the bond that we’ve built in the fire of adversity growing up with nothing.” — BYU defensive coordinator Ilaisa Tuiaki, who announced his resignation Sunday after the Cougars downed Stanford 35-26 on Saturday

The news comes a day after the Cougars finished the season with a 7-5 record after a 35-26 win over Stanford. BYU Athletics officially announced Tuiaki is stepping down but it is unlikely that Tuiaki will coach in the Cougars’ bowl game, which has not been announced and might not be known until next Sunday.

Tuiaki thanked head coach Kalani Sitake and Sitake’s wife and children in his posts, calling Sitake “my friend, my brother and mentor.”

He noted that “contrary to BYU fan belief,” he and the head coach are not related.

“This job can’t sever the bond that we’ve built in the fire of adversity growing up with nothing,” Tuiaki noted.

Sitake and Tuiaki were coaching at Oregon State when Sitake got the head job to replace Bronco Mendenhall, and tabbed his longtime friend as his first defensive coordinator in Provo.

“It’s not possible for me to express my true appreciation for Ilaisa and what he means to me as a friend, brother and coach,” Sitake said in a statement. “Not only have we coached together more than a decade, but he and his wife Viola and their kids are like family to me and Timberly. I can’t offer enough thanks to him for all he has done to help build our football program as our defensive coordinator the past seven years.

“His dedication is unquestioned and his trustworthiness is unmatched. He is completely selfless in how he handles everything he does. I have seen how much of an impact ‘Ilaisa has had on the lives of the players he has coached and how much he genuinely cares about them and about their well-being. He will always be family to me and to so many others. I know he will continue to have that kind of impact as a coach as he takes on his next challenge.”

The first five years of Tuiaki’s tenure were fairly successful, but the Cougars’ defense has struggled the past two seasons, and Tuiaki has taken the brunt of the blame from BYU fans.

After a 52-35 loss to Arkansas on Oct. 15 in which BYU’s defense surrendered 52 points, 34 first downs and 644 total yards, Tuiaki met with Sitake the following Monday morning and offered to resign. However, Sitake persuaded him to stay and take over defensive line coaching duties, noting that the program needed “all hands on deck” to get out of its slide.

Sitake called the defensive plays in the 41-14 loss at Liberty on Oct. 22, but the unit was still a mess and offered little resistance to a Liberty backup quarterback.

Even during the Cougars’ recent three-game winning streak, the defense hasn’t returned to early season form when it looked solid in victories over South Florida and Baylor.

Tuiaki also thanked his defensive staff “who have worked countless hours with me” and praised them for their friendship and loyalty.

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“Thank you to all of the players through the years that I’ve had a chance to coach and recruit to BYU,” Tuiaki wrote. “… I want you players to know that I gave you my best.”

Tuiaki’s hiring in 2016 was met with skepticism in some circles, but he and Sitake put together defenses that ranked in the top 50 in the country in scoring defense his first five season.

This year, the Cougars are 101st in scoring defense (30.0 points per game) and 93rd in total defense (409.7 yards per game). They are second-to-last in team sacks (130th), even after getting three against Stanford to bring their season total to 13.

Tuiaki’s bend-but-don’t-break defensive philosophy where he would often drop eight defenders into pass coverage often drew the ire of BYU fans in recent years.

“To the passionate Cougar fan base, thank you for the memories,” he wrote. “I have made a lot of friends and met a lot of awesome people during my time here.”

What Tuiaki’s resignation means to BYU’s other defensive coaches is unclear. However, new coordinators are often given the opportunity to assemble their own staffs in college football, so there is a lot of uncertainty surrounding the defensive side of the program right now.