We all know the wedding guest golden rule - never wear white to a ceremony, so you don't upstage the bride.
Sometimes that's ignored if the bridesmaid is also in white - and the bride has chosen the dresses herself!
Remember Pippa Middleton at her sister Kate's wedding to Prince William?
Pippa Middleton at the Royal Wedding
But when it's the mother-of-the-groom? It's definitely unusual - as is wearing an ivory, full-length gown that could easily be mistaken for a wedding dress.
But that's exactly what happened at one wedding that's been featured on Reddit.
The groom shared his wedding pictures on Facebook and they were re-posted on social media with people questioning if it was socially acceptable for the mum to wear such an outfit.
Unsurprisingly, people overwhelmingly thought the mum's choice of dress was unusual and disrespectful to her new daughter-in-law.
One said, "I feel bad for the bride."
A second was more blunt and said, "I'm gonna vomit. Girl, get it annulled."
A third follower noticed that the mum was also holding a posy of flowers in her photos with her son which did not go down well, and the dress appears to have a train.
"White dress AND a bouquet of flowers?" said the commenter. "Jeez, how can people be so blind to their inappropriate behaviour!"
Sadly others revealed that this wasn't the first time they had seen something similar.
"This happens a lot," said one. "And to be honest I prefer the mum's dress to the bride's which would be devastating if you were getting married and your mother-in-law outshone you!"
But others disagreed, saying that the whole thing could have been taken out of context.
"Maybe there's a story behind this," one said. "If the bride didn't mind, why should we care?"
Would you be upset if this was your wedding?