It'd take some internet sleuthing to figure it out but it spilled out publicly a touch when she commented on photos of her ex on instagram, and received the response
Around the time this happened, I did a little poking around and found out from people discussing it (as this never really gained traction with any big news sources) that the ex's sister had a detailed instagram post describing how her sister's unnamed famous ex had been psychologically abusive, tried to isolate her from her family, and on the day of the sister's wedding sent her a ***** in the mail after everything - taken as harassment.
A lot of the materials involved have been deleted now because, you know, internet, but I'm really inclined to believe it given, if it were some kind of lie, you'd think they'd be naming names, going to the press or trying to extort money. Just comes off like people who want to be left alone to me.