AITA for telling my ex’s new girlfriend he’s cheating on her?

Hello there — this one’s a bit complicated. My ex and I were together for nearly 11 years. It’s been about a year since we officially broke up, but we’ve still been involved — including seeing each other regularly and even spending the night together. Recently, I discovered something that made me realize just how little he’s changed.

I found out that he saved my contact under a man’s name in his phone. I couldn’t help but laugh at the irony — during our relationship, I used to find other women’s names in his phone, and now he’s hiding me in the same way.

It turns out he has a new girlfriend. She has me blocked, yet I know she watches my social media (she unblocks me and blocks me again). What she doesn’t know is that I have screenshots of our recent conversations and even a video from one of our recent encounters. More importantly — I was recently pregnant with his child, and he never told her about it. When I’ve asked him directly if he’s seeing someone, he completely denies her existence.

I’m at a crossroads. I’m not interested in getting back with him — in fact, discovering this has made it crystal clear that he hasn’t changed. But part of me feels like she deserves to know what’s really going on. Not out of spite, but because I’ve lived through the lies and betrayal he’s capable of, and I wouldn’t wish that confusion and pain on anyone else.

So here’s my question: Would I be wrong for telling her the truth about what’s been going on between us? Do I stay silent and let her figure it out like I once had to… or do I say something and risk being seen as “the bitter ex”?