The woman, from Scotland, was fuming when her newly engaged sibling announced plans to tie the knot in 2024 just like her.
Writing in to the Girls Overheard podcast, she said she wanted the year to be “all about her” and now fears her sister will steal the spotlight.
She said: “Me and my partner were getting married in July this year but due to unforeseen circumstances we’ve had to postpone until next July.
“So we’ve got most of our planning done, venue booked etc.
“About a month ago or so my mum mentioned that my sister, who is also engaged, was thinking of having her wedding next year also.
“This really upset me as she’s a lot older than me, had been married previously and to also mention every big event in my life has been diminished by my sister.
“The one thing I thought could be about me would now be turning into us or more realistically, all about her.
“I told my mum and my sister my concerns. My mum’s initial response was ‘it’s not her fault your unforeseen circumstances cropped up and that’s why you’re not getting married this year.’
“Is it still wrong of me to say I still don’t want her getting married the same year as me?”
The video has racked up more than 32,000 views, with social media users divided.
Some have insisted the bride-to-be is being a “diva” and can’t block off a whole year.
One said: “A wedding is one day, I don’t think you can claim the whole year as your own.”
Another wrote: “Yip unacceptable, sounds like she’s a diva.”
A third added: “What a spoiled brat, life’s too short for this s***.”
And a fourth agreed: “So unreasonable, especially if your sister is older. She will probably want to settle and have a family so she can’t be expected to push back.”
But some have agreed with the woman that she should have her time to shine.
One said: “I would be fuming if my sister got married within a few months of me because the build up with the hen etc is fun.”
Meanwhile, another added: “Absolutely not. I have a sister who would ruin all I would do, I feel you.”