A woman on Reddit is furious with her sister after she made an insensitive joke about how her ex-fiancé ran off with his pregnant mistress on her wedding day. Now, she refuses to buy her sister her dream wedding dress, even though she promised to.

On Reddit, the woman explained that on her "wedding day back in 2017," her "former fiancé abandoned" her and "ran away with his pregnant mistress." The jilted bride was traumatized.

"This was truly a turning point in my life. My family has always been there for me so I kept close to them," she wrote via her Reddit post.

"My younger sister is currently engaged and her wedding will be in a few months. She's struggling with money so I decided to help her and her fiancé and pay for the wedding dress. This allowed her to be able to buy her dream wedding gown that costs $7,000. It's a lot for a dress but she literally cried because she wanted it," she continued.

However, at dinner a few days before they were scheduled to purchase the bridal gown, the woman's sister made an insensitive joke, sparking a sibling feud.

READ MORE: Bride Refuses to Show Wedding Dress Pic to ‘Competitive’ Cousin

"My aunt was asking my sister about the wedding and my sister said that everything was going according to plan and then casually laughed and said 'let's just hope he won't run away with a pregnant mistress or something on our wedding day.' I was blown away completely. She laughed and aunt laughed too as if this was a joke. She was basically mocking what happened to me at my wedding," she recalled.

The woman started screaming at her sister and called her an "idiot" while her parents tried to calm her. She then abruptly left the dinner.

"My aunt remained seated and my cousin asked me to calm down and drink some water but I grabbed my stuff and as I was getting ready, I told my sister she was getting 0 dollars for her dream wedding dress ... then I walked out. I heard louder commotion as I walked and my dad and cousin followed me outside trying to talk but I asked to be left alone," she continued.

Later, her parents told her she was "too harsh" on her sister "over a joke," and that she knows her sister has a "dark sense of humor."

"They said she's been crying after I decided to back out of helping her and said this [would] ruin her wedding. They want me to reconsider my decision since it might damage my relationship with my sister but I refused," she concluded.

READ MORE: ‘Miserable’ Woman Doesn’t Want Husband to Walk Sister Down Aisle

Users in the comments section rallied behind the woman, telling her she was right to feel hurt by her sister's comment.

"Serious lack of self-awareness and simple respect from this sister. Charged remarks come with charged consequences," one person wrote.

"Let's all joke about someone's trauma, and then get mad at them when they react exactly how you'd expect someone with trauma to react," another commented.

"She was crying over a dress. She should have been crying with remorse for how she hurt you. All she cares about is 'HER DAY and HER DRESS' and YOUR wallet. Tell her to pound sand and if anyone in your family gives you shit, tell them the same. Tell them that in 10 years, IF she’s matured and can sincerely apologize, you MIGHT forgive her and you MIGHT consider a nice anniversary gift. If the marriage lasts that long," someone else weighed in.

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