When someone more junior than the others got a promotion, gossip will fly. In fact, I would say anyone who was promoted, are bound to attract jealousy, anger, etc.
“I have been here for 2 years and she just joined 6 months ago. What is this?”
“I am leaving, this company is not recognising my efforts.”
“She must have did something with the boss.”
Not withstanding the fact that there are people who really don’t deserve a promotion, there are those who work hard for it. Acknowledge that, shall we?