An enraged bride booted her big sister from her wedding ceremony after she showed up wearing "practically a bridal gown" on the big day.

Taking to Reddit, the newlywed named Ashleigh blasted her spotlight-stealing sibling, who she says "decided to test me in the worst way possible."

"It's exhausting, but I figured she'd at least behave at my wedding," the bride wrote. "We've never been close, she's always tried to one-up me, even during family events."

Ashley says she gave out her dress code with months of notice and she "made it very clear: nobody wears white but me."

"It wasn't negotiable," she declared in her Reddit post.

Her older sister subsequently gave her some attitude about the standard request, saying that the bride was being "insecure" and too focused on outdated tradition.

"I told her that whether or not she agreed, she needed to respect it," Ashley wrote. "The morning of the wedding, she showed up wearing a floor-length, lace white dress. It was practically a bridal gown."

"My heart dropped, and I straight-up asked her what the hell she was thinking. She said, 'It's not that white, and besides, no one will care.'"

Standing up for herself, the bride told her sister to change or hit the road, which led to a meltdown from her sister.

"She threw a tantrum about how I was ruining her day and stormed off, telling everyone I was being 'bridezilla,'" Ashley wrote.

"So, I told the staff not to let her back in unless she changed. She never came back, and now she's telling everyone I ruined the relationship for good."

Now, the bride is getting grief from her parents for kicking her sister out of the venue, despite feeling like the white dress "was a deliberate choice to sabotage my day."

Online, however, many sided with the bride over the dress diss.

"Your sister disrespected your clear dress instructions and showed up in a white gown almost identical to a wedding dress," one commented. "She was trying to steal the spotlight at your wedding. You were right to uphold your boundaries and not let her ruin your day."

"It's universally understood white is reserved for the bride," added another.

"Your sister clearly knew that a white dress would be a problem: it's common knowledge, it was in the invitation + you told her personally about it beforehand and yet she did it anyway," a third wrote.