When do you tell your friend that his girlfriend js a gold-digger?

Long story short, one of my friends has been in a relationship for about 2 months. Personality-wise, she's basically a blow-up doll who wears too much makeup, acts like a child for attention, and yells everything she says. She's universally hated by our friend group.
Anyway, the friend is going to make a ****ton of money right out of college and, per inside sources (his ex who works with her), she's been bragging to her coworkers about how he's inadequate, but she's sticking around because of the money. She's also told her coworkers about how he's too small for her.
Now, at what point do I tell him that she is using him unapoligetically? It feels ****ty to keep it to myself but I also don't want to interfere in his relationship.
Edit: looks like I ****ed up. I guess I have some thinking to do.


Source.