Ex boyfriend is engaged a month after breakup…..

I recently found out that my ex, who I broke up with in August, is engaged to another woman. Obviously this is super suspicious timing, and he must have been cheating on both of us. He was even hitting me up to hook up last week, saying I was the best sex of his life. I want to somehow anonymously tell her about his cheating without getting myself involved (because I don’t feel comfortable and don’t want to risk her blaming me or him coming after me for telling). Does anyone have any ideas? I also don’t follow her on any socials so I can’t DM her, but I did find her Tik Tok.