I haven't said anything to him yet. One side of me says this is a huge accomplishment for him and he's been working towards this promotion for years. The other side says let tbe OW validate him.
I can't tell you the right answer; that is in your heart and head.
Me personally tells my W when she has some great achievement something to the effect of "That is really great." She fishes for compliments a lot, always has, but im not going to stroke her ego with effusive praise at this time. Just give her a simple acknowledgement of her achievement without giving an ego boost. That is what I do.
Validate feelings, not things. So he sent you a grade for his class. No validation needed, but acknowledgement that he accomplished something is appropriate I think. Hope that is helpful!
Me40; W38; S12; D9 BD11/19/2018 D filed 12/20/18 D Final 7/2020 Being the best example I know how for my kids to see.