My boss gave my promotion to his nephew. Then asked ME to train him for the job I was supposed to get.

So I’ve been at this company for six years. Started as an entry-level assistant, worked my way up, took on extra projects nobody wanted, stayed late during two different rounds of layoffs when everyone else quit. My manager, we’ll call him Greg, has told me literally every review for the past two years that a senior position was “coming for me soon.” I believed him. I planned my whole year around it.
Three weeks ago, the position finally opens up. I put in my application, do the interview, feel great about it. Greg tells me afterward, quote, “you’re exactly who we need for this.”
Last Monday, they announce the new senior analyst. It’s not me. It’s a twenty-four-year-old named Connor who started four months ago and has zero relevant experience. I’m sitting there confused, thinking maybe there’s been some mix-up, until I hear someone in the break room mention that Connor is Greg’s sister’s kid.
His nephew. Greg gave the job I was promised for two years to his own nephew, who has been at the company for less time than most people’s coffee orders take to memorize.
But here’s the part that actually made me want to scream into a pillow. Two days later, Greg pulls me aside and asks if I can “show Connor the ropes” for the next month, since I know the role better than anyone. He said it with a straight face. He wants me to train the guy who took my job, for free, on top of my current workload, because I’m apparently the most qualified person for a position I didn’t get.
I asked Greg directly why Connor was chosen over me. He said, and I’m quoting this exactly, “he’s got a lot of potential, and honestly, family loyalty means something to me.” He said that out loud. To my face. As a real reason.
I haven’t agreed to train Connor yet. I told Greg I needed to think about it, which visibly annoyed him, like I was supposed to just say yes immediately and be grateful for the opportunity to build my own replacement’s resume.
My coworkers have been messaging me all week saying I should just quietly start applying elsewhere and let Connor sink or swim without me. My partner thinks I should flat out refuse to train him and make Greg explain to HR why the most experienced person on the team won’t help.
I have a meeting with Greg tomorrow morning where he expects an answer.
So tell me, am I wrong for considering saying no, or is nepotism just something I need to accept and work around?
Follow for the update, because I already know what I’m saying tomorrow.