How should I handle my ex-husband only gifting assets to our son and not our daughter?

Ex (61M) and I (57F) divorced 12 years ago. I had full custody of our 2 kids (now 25M and 22F) until they went to college. Won’t get into divorce details but let’s just say he was far from a perfect husband and father.

My ex and my son have a strong relationship. However my ex and my daughter haven’t talked in 10 years which was her decision that I respect entirely.

In our divorce, among other assets, there was one illiquid asset that we split 50/50 as it could not be sold at the time of the divorce. Since then we’ve held it and haven’t looked for a buyer.

Last year my ex transferred his half of the asset to my son. We are closing on a sale later this month and will net 260k - 130k for me and 130k for our son.

My problem with this is that this was a marital asset that we split and I don’t think it’s fair for my ex to transfer his half to our son with nothing for our daughter.

I’d like to gift my daughter 130k to make up for this. I mentioned this to my son and he was upset, saying that I’m overstepping and it’s not my place to play judge, that I’m devaluing his dad’s gift, taking away from his future inheritance, etc. Son also made a comment about how I pay daughter’s rent which is true. After college my son (lucrative field) always paid his own rent but I’m currently paying daughter’s (non-lucrative field) rent. It’s been 5 months now and I’m not sure when or if I’ll stop.

I’m torn because I want to do what I think is fair but I don’t want my son resenting me. I’m also concerned because this might not be the last time my ex gifts to my son. I wouldn’t be surprised if he cut our daughter out of his will entirely.

How should I handle both this situation and future situations?

My NW is around $10M (independent consultant in niche industry). No idea about my ex’s (retired engineer) but I’d guess $5-10M