Various wedding 'rules' have relaxed over the years, but if there's one thing that is still considered the ultimate faux pas when attending a wedding it's wearing white when you're not the bride.
But one guest apparently took it a step further by showing up to her friends wedding wearing a literal wedding gown.
A photo of the guest with her partner - also dressed in his wedding best - was shared to popular Reddit forum 'Wedding shaming', with the caption "she looks absolutely gorgeous... except she's not the bride... you had ONE JOB."
The post has racked up hundreds of comments with people in complete bewilderment that anyone would choose this as a suitable outfit for somebody else's big day.
"This isn't even just an inappropriate white dress. It's a wedding gown. It even has a train," wrote one person. "It would be a shame if someone accidentally spilt a glass of Cabernet on that," to which someone replied: "thats what bridesmaids are for".
"I refuse to believe this is anything other than the bride and groom," wrote another.
To make things even better, the Reddit poster then managed to track down a picture said to show the guest next to the bride, and it's difficult to tell which is which.
It's not the only inappropriate wedding outfit to make headlines.
Earlier this year a guest was accused of trying to "upstage the bride" with a sheer, floor-length gown made of red lace.