A.J. Klein spent four years learning from Sean McDermott, the defensive coordinator who helped get Klein ready to assume a full-time starter's role.
Turns out both men were headed for bigger things.
McDermott, who spent six years at the head of the Carolina Panthers defense, was hired as the head coach in Buffalo in January, a mere two months before Klein signed with New Orleans as a free agent.
Now, the pair are getting ready to face off against each other Sunday.
"A.J. Klein — he's a guy I'm partial to," McDermott said. "(I) know what he brings to the table in terms of his play and what he brings to the overall defense."
Two years into McDermott's tenure in Carolina, the Panthers drafted Klein, and the coordinator helped the young linebacker learn the NFL game from a different perspective.
"He taught me how to understand the why," Klein said. "Not just, 'Hey, this is three-deep; this is quarters; this is pressure.' He helped me understand the why, understand the game and how it's played from the coordinator mindset."
Klein learned to lead from the middle linebacker spot, and the Saints are reaping the benefits now.
After signing in New Orleans, Klein was voted a team captain, has played every single defensive snap for the Saints so far and leads the team with 41 tackles, along with a sack and four passes defended.
McDermott was happy to see his former pupil get a chance to start full-time. Klein, obviously, was stuck behind Luke Kuechly in Carolina, and the glimpses Klein gave of what he could do as a starter when Kuechly was injured were enough to convince his coordinator that Klein was ready for more.
"I was happy for him," McDermott said. "Selfishly, I'd like him on my team, but outside of that, when he got picked up, it didn't surprise me. He'd been waiting for an opportunity like this. When he started in Carolina. ... He always did a great job."
McDermott didn't say whether the Bills wanted to sign Klein in free agency, noting that the Saints scooped up their former NFC South rival on the first day he was available.
But both men are thriving now in their new spots. Klein, like he envisioned, is at the head of a surprising Saints defense, and McDermott has led the Bills to an unexpected 5-3 record.
Klein credits McDermott for getting him ready for the role he's playing now.
"From when I was a rookie coming in, he always had confidence in me," Klein said. "It allowed me to have self-confidence and continue to grow as a player. Obviously, it led to where I am now."