When one person gets elevated, it throws off the power balance of a relationship and people have to readjust.
"In the workplace among peers, there is a sense of equality that we are all in this together," said Rebecca Chory, an associate professor at Frostburg State University who studies organizational behavior and workplace relationships. "But when one person moves up, the equality part is no longer there."
Address the elephant in the room
The relationship is going to change when one person gets promoted — there's no denying that. The key is to recognize the shift and map out a plan to move forward.
Have a frank — and likely a little uncomfortable — conversation about what has happened and what happens next.
"As a new manager, you have to remember that you are no longer peers," said Amy Cooper Hakim, an industrial-organizational psychology practitioner and workplace expert.
Be aware that even if one person in the relationship wasn't looking to get promoted, there will likely be some negative feelings, including jealousy.
"The only way those negative emotions can be quelled is by talking them through," said Denise Dudley, a behavioral psychologist.
It can help to ask for support in your new endeavor. "Show vulnerability," she said. "Say: 'This could get weird, but I don't want it to and I am looking for your support.'"
Lead by example
As the new manager, you set the tone of how the new relationship will work with your former peers.
And don't get fooled into acting tough to gain respect, warned Cooper Hakim.
"It doesn't work. Lead by example by being positive and friendly, with a kind tone while still holding people accountable." The key is to have empathy with how your peers might feel about the situation.
Find a new sounding board
We all need someone at work to bounce ideas off of or to vent to. But when you get promoted, it's a good idea to find a new confidant.
"That could mean you cultivate a new relationship with another manager," said Dudley.
You will likely be privy to more projects and confidential information that shouldn't be discussed.
"You are now the manager and have certain tasks and obligations to the organization," said Cooper Hakim.
Know that people are watching
People are going to assume there will be some favoritism, so try to avoid giving any impression that could be happening.
"In general, you are likely not going to hang out in the same way before the promotion, it just gets very sticky," said Cooper Hakim.
That means cutting back on the private chit-chats you used to have in the kitchen, and the daily lunches or coffee runs might have to stop or include more people to avoid any perception of partiality.
"No matter what, people will be looking for ways you are practicing favoritism," said Dudley. "You have to ride that through by being so fair and objective that people eventually settle down."
Friends should also note that just because they are close with the now-manager, that doesn't mean they should be asking for any favors or expect special treatment.
The friendship can end
Sometimes, a friendship won't be able to survive one person's move up the org chart -- and that's OK.
"The friendship may fall apart and break up, and in some ways, that solves a lot of the problem," said Chory. "You won't have the tension if you aren't as friendly and disengage."