You got the promotion. Now you're the boss of the people who used to grab lunch with you, vent about the old manager with you, and tell you things they'd never say to management. And at least one of them is treating you exactly the same as before. Calling you by your first name in meetings where everyone else has shifted their tone. Asking you for favors they'd never ask a "real" manager. Bringing the same irreverent energy that used to be your shared language. It was fine in February. Now it's a problem—and you can feel the authority you're supposed to have slipping through your hands every time you let it go unchecked.
The peer-to-manager transition fails more often than it should, and it fails for a structural reason: the relationship has two incompatible histories running simultaneously. Your former peer has a version of you in their head—a colleague, a confidant, maybe a friend—that predates your authority over them. You have a version of the relationship that involves easy familiarity and zero formal power. Neither version works anymore, but nobody called time on the old one.
Most managers try to thread this needle with informality—treating former peers "the same as before"—and end up with neither the friendship nor the authority. The instinct is understandable. You don't want to become someone you'd have rolled your eyes at two months ago. But the problem isn't that you're now in a formal role. The problem is that the relationship hasn't been renegotiated. Friendships work on unspoken norms. Management requires explicit ones.
The reset needs to happen directly, not implicitly. Sit down one-on-one with each former peer early in your tenure and name the change out loud: "I know this is a weird transition. We've worked side by side and I want to keep that trust. And I also want to be honest that my job is different now. I'll be giving you feedback, evaluating your work, and making decisions that affect you. I think we can handle that—but I'd rather say it out loud than let it become the thing we're both avoiding."
That conversation does two things. It models the directness you want in the relationship going forward. And it gives your former peer a clean opening to signal how they're going to approach this—information you need early, because the ones who deflect or laugh it off are telling you something important.
For the specific person who's acting like nothing changed: name the behavior early and precisely. Not "you need to respect my role" (vague, defensive) but "when you undercut my call in the team meeting this morning, it makes it harder for me to do my job—and I need that to not happen again." You're not asking them to stop liking you. You're asking them to separate the friendship from the working relationship. The good ones can do both. The ones who can't will show you that quickly.
Don't delay these conversations. Every week you wait, the informal dynamic calcifies. Your other team members are also watching to see how you handle it—and if they see the former peer getting away with boundary violations you'd address with anyone else, they'll calibrate their own behavior accordingly. Fairness requires consistency, and consistency requires acting early.
Watch for the former peer who was in competition with you for this role. That dynamic adds a layer that pure friendship transitions don't have. Some people handle it gracefully; others carry the resentment as a slow burn that shows up as subtle undermining, eye rolls during your presentations, or conspicuously not endorsing your decisions in front of leadership. Name it privately and early. Give them the chance to be direct with you. But don't let it fester—and don't let loyalty to the old relationship make you slow to act when the behavior becomes a performance issue.
Some former peer relationships don't survive the promotion—and that's not always a failure. If the dynamic isn't adjusting after you've been direct, you may be managing a loyalty problem rather than a transition problem. There's a difference between a peer who needs time to calibrate and one who fundamentally resents your advancement. The first is manageable. The second requires the same documentation and intervention you'd use with any employee whose behavior is affecting team performance.
Name the change early, be direct about the new dynamic, and manage like a manager—the longer you wait to establish your role, the harder it gets to establish it at all.