Kingsbury, now head coach of the Arizona Cardinals, coached both starting quarterbacks -- Kansas City's Patrick Mahomes and Cleveland's Baker Mayfield -- in consecutive seasons as head coach at Texas Tech.
When the two former Red Raiders square off for a chance to play in the AFC Championship Game, Kingsbury will sit back and relish the moment.
"It's kind of like being a big brother, I guess," Kingsbury said. "I just sit back as a fan now and try to enjoy the success those guys are having. Just to be around those guys, have a small part in anything that they've been able to become as a quarterback, I take a lot of pride in that and those guys know that."
How much credit Kingsbury can be given for their NFL success is hard to quantify, but this much is certain: He gave both a chance to be Power 5 quarterbacks.
Before they were NFL stars with commercials and mega-sponsorships, they were three-star recruits coming out of the quarterback hot bed that is Texas -- Mahomes from Whitehouse and Mayfield from Lake Travis, where he won a state championship.
Neither splashed on the recruiting scene for various reasons.
Mahomes' recruitment was full of uncertainty because schools weren't sure whether he'd opt to play professional baseball instead of college football. But getting drafted in the 37th round by the Detroit Tigers cemented Mahomes' decision to play football. Kingsbury began recruiting Mahomes while he was the offensive coordinator at Texas A&M in 2012 and that continued when Texas Tech hired him in December 2012. Mahomes, who also had offers from Oklahoma State and Rice, visited Texas Tech in the spring of 2013, before his senior season, and committed in person to Kingsbury, Whitehouse coach Adam Cook recalled.
"Kliff was pretty high on him," Cook said. "I know that for Kliff, it was important that Patrick knew that once he committed that he took all of his other quarterbacks off his board. He made sure that he never wavered, even though there was the speculation of him going into the [MLB] draft."
Questions hovered over Mayfield's recruitment because of his size. He was 6-foot-1 and 190 pounds as a senior. He developed physically late, not until he was 18 and 19, said Hank Carter, Mayfield's coach at Lake Travis High School. By then, though, the top tier of Texas' college programs already had their quarterbacks set. Only Florida Atlantic, New Mexico and Rice offered Mayfield, but Carter remembered Mayfield and his family deciding to pass on those scholarships in favor of trying to walk on at a Power 5 school.
"I was a little bit surprised that he didn't take them but also knew that he had been really clear with us he wanted to play big-time college football," Carter said.
Texas Tech -- both before Kingsbury arrived in 2013 and after -- had developed a reputation around the state as being a good place for under-recruited quarterbacks to play because of how much the Red Raiders threw the ball.
"Back then, you knew you were gonna throw for a million yards," Carter said. "It's kind of like you have a chance to really show a lot of your potential because you're going to be throwing the ball 40 times a game and so I've seen a lot of kids that were slightly under- recruited go through that route and it turned out well for them."
As it did for Mahomes and Mayfield, who, serendipitously, were separated in Lubbock by just a couple of months. Mayfield even hosted Mahomes on his official recruiting visit. Mayfield played at Texas Tech as a freshman in 2013 -- earning Big 12 Freshman Offensive Player of the Year honors -- before transferring to Oklahoma that December. Mahomes enrolled in February 2014.
By 2015, both were starting -- Mahomes for Kingsbury and Mayfield for the Sooners. A year later, they faced each other in a 66-59 barn burner, combining to break several records, including the most combined yards in an NCAA game.
Sunday isn't the first time they've faced each other in the NFL but it's the most important.
"It is always fun to play friendly competition and playing against people you are familiar with," Mayfield said. "He has gotten me so far in the league so I have to see what I can do."
Said Mahomes: "Known him for a long time, since I was a senior in high school, and to be able to play on this stage is going to be special. I mean, he went to Oklahoma, I went to Texas Tech, so he got the better of me in college, so I'll try to do my best to win in the NFL."
Kingsbury has kept tabs on his former quarterbacks.
On Mayfield: "I really think [Browns coach Kevin] Stefanski and him are a perfect marriage with his skill set and you know he's one of the brighter players I've ever been around, and obviously has a lot of passion for the game. His teammates love him."
On Mahomes: "Patrick is, he's ... nobody's ever seen anything like him and he continues to just kind of wow and amaze, and watching his leadership evolve, and where he's taking that team, it's just been fun and makes Sundays fun when I get a chance to watch some of those guys."
And nearing a decade after their recruitment, the high school coaches for both believe the lack of recruiting attention each received has stuck with them.
"Part of this is the reason Baker is who he is is because of the way that he had to fight and scratch and claw for everything he's gotten," Carter said. "It probably worked out how it's supposed to."
Said Cook: "Definitely two guys who are meeting up here for a playoff game in the NFL that probably played with a little bit of a chip on their shoulder throughout a lot of their career, where you know they're a 'system quarterback' or they're 'too short' to play there. And, you know, it's gonna be pretty fun to watch."