A "furious" groom on Reddit can't forgive his sister for ruining "one of the happiest moments" of his life.

The groom explained that he had a romantic, perfectly planned out proposal ready for his fiancée including flowers, a picnic, a beach background and a photographer to capture the moment.

"When the day came, my sister (32F) insisted on tagging along. She said she wanted to take a few 'candid' photos of us before the proposal. I was hesitant but agreed, thinking it might make the moment more special," he shared in his post. "Big mistake."

The proposal quickly went downhill thanks to the groom's sister's odd behavior.

READ MORE: Woman Upset Half-Sister Asked to Wear Her Dead Mother's Jewelry

"As we reached the spot, my sister started acting weird, making snarky comments and trying to direct the whole scene like a movie. My girlfriend could sense something was off, and the mood was getting ruined," he revealed.

"Then, out of nowhere, my sister grabbed the ring box from my pocket and yelled, 'Surprise! Look what he's going to do!' My girlfriend was shocked, and I was furious," the man went on.

He said that he tried to salvage the proposal he had planned, but the moment was "tainted" by his sister's outburst.

"My girlfriend said yes, but we both felt the proposal was ruined," he said.

The groom confronted his sister after the proposal and she told him he was "overreacting."

"She just laughed it off, saying she was 'just trying to help,'" he continued.

But the wedding drama didn't stop there.

"Fast forward to our wedding planning, and my fiancée and I decided not to invite my sister. We wanted our day to be about us, without any unnecessary drama. When my family found out, they were furious," the groom said.

"My parents called me heartless, and my sister is playing the victim, saying I'm tearing the family apart over a 'little joke,'" he added.

Reddit commenters were appalled by the groom's sister's actions.

"What she did is so ludicrous that my first reaction was that perhaps this post isn't real, no one could be that obtuse. I don't blame you one bit for not wanting her at your wedding," one person wrote.

"What’s the joke? And how was she helping? Your sister is beyond out of line. I'm so sorry you have to deal with her nonsense," another person agreed.

"You and your fiancee need to present a united front and make it clear that your sister will not be invited. She already ruined your proposal, and you don't want her to ruin your wedding," someone else said.

Another person called the sister's behavior "unhinged."

However, one person criticized the groom for allowing his sister to come to the proposal in the first place.

"A bit of a dumbass for allowing her to tag along for the proposal. Never mind that the proposal should have been a private affair between you and your girlfriend, but you admitted in your own post that your sister has done outlandish things at the most inappropriate times to seek attention, so you were quite naive to think she would behave when you planned to propose," they said.

Celebrity Couples Who Secretly Got Married

Below, discover 25 famous pairs who tied the knot in secret, private wedding ceremonies away from the glare of paparazzi cameras.

Gallery Credit: Michele Bird

More From WKFR