Petty Betty at its finest.

A significant other’s ex is the last thing someone wants to think about on their wedding day. Sadly for one bride, her sister-in-law sneakily involved the groom’s ex — without her knowing — by livestreaming her brother’s entire wedding to later show her.

The devastated bride took to the r/weddingdrama forum on Reddit to vent about how her husband’s sister betrayed her — and sheesh, this one is a doozy.

The original poster shared that her now-husband — with whom she has been together for eight years, married for two — has a daughter from a previous marriage. The ex-wife has been in and out of the picture due to her addiction issues for the past several years.

This happy couple said “I do,” never realizing their special moment would be sent to the groom’s ex.

See Full Page