His brother has reconnected with his ex years after a nasty divorce. How can he stop it?

“Six years ago my brother went through a nasty divorce. They fought in court, she took their home and they hadn’t talked for years. Fast-forward to March and they matched on an app. They’ve gone on a few dates and he wants to get back together. I’m anxious because I remember what happened and I know it’s going to be a disaster for everyone around them. How can I intervene?”