A woman who does not want to attend her sister's wedding is not wrong because of the highly unusual circumstances, said a relationship expert and users of Reddit in response to the woman's post.

"AITA for refusing to attend my sister's wedding after she secretly dated and got engaged to my ex-fiancé?" asked user "AlisonVio" in a July 8 post on the "Am I the A--hole" subreddit.

In the post, the woman warned readers to "buckle up, because this is a roller coaster." 

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She said she's a 28-year-old woman who was engaged to "Mike" for two years before they broke up just three months before their planned wedding last summer. 

"I found out he had been cheating on me with someone else," the woman wrote. "I called off the wedding immediately."

couple sitting together

The Reddit user said she and her fiancé broke up after he cheated on her before their wedding – and now the man is engaged to her younger sister.   (iStock)

"Mike," she said, moved away after the breakup, and AlisonVio said that she "thought that was the end of it." 

She added, "I was heartbroken, but I slowly started to move on with my life" — until last month.  

"I get a call from my younger sister 'Lily' (25F) saying she has exciting news and wants me to come over to our parents' house for dinner to share it," AlisonVio wrote. 

"My head was spinning. I felt like I was going to pass out."

She continued, "When I arrived, Lily and my parents were all smiles, and she drops the bombshell: She's engaged. To Mike."

AlisonVio wrote of the shock, "My head was spinning. I felt like I was going to pass out." 

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She then learned that "Lily and Mike had been secretly dating for the past year, and now they were engaged," and that her parents had "known about it for months" but opted not to tell her.

"They actually thought I'd be happy for them eventually," AlisonVio said. 

Her sister, on the other hand, "tried to justify it by saying she and Mike fell in love after our breakup and that their relationship is meant to be." The sister claimed that she did not begin dating Mike until after the breakup.

A smashed three-tier wedding cake with fallen bride and groom cake toppers.

The woman who shared her story said her wedding to "Mike" was called off just months before it was to take place last summer. But now her sister is engaged to the same man — and plans on marrying him soon. (iStock)

"I felt betrayed on so many levels," AlisonVio said, adding, "I told them all that I wanted nothing to do with their wedding and stormed out." 

This did not go over well, she relayed.

"My parents and Lily have been bombarding me with calls and texts, calling me selfish and saying I'm overreacting."

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The woman wrote, "They claim that true love is rare and I should be supportive of Lily's happiness. Now, the wedding is in a few months, and the pressure is on … My parents have even threatened to cut me off financially if I don't attend," AlisonVio said. 

Lily, she said, even asked her to be her maid of honor, "claiming she wants to mend our relationship." 

Wrote AlisonVio on Reddit, "This request has left me torn — I don't want to ruin our family dynamic further, but I can't shake the hurt and betrayal I feel." 

A split photo of two sisters fighting that is next to an image of the Reddit logo shown on an iPhone.

AlisonVio (not pictured) said her sister asked her to be in the wedding as a way to "mend" their fractured relationship.  (iStock/Getty Images)

Her friends, conversely, are split about what AlisonVio should do. 

"Some friends think I should go to keep the peace and show I'm over it, while others are appalled and say I have every right to be angry and to stay away," she said. 

"It's the wedding of her ex-fiancé who cheated on her." 

"So," she asked others on social media, "AITA for refusing to attend my sister's wedding after she secretly dated and got engaged to my ex-fiancé?"

Nicole Moore, a California-based relationship expert and certified life coach, told Fox News Digital that AlisonVio "is absolutely not wrong to not want to go to her sister's wedding because it's not just her sister's wedding. It's the wedding of her ex-fiancé who cheated on her." 

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"Most people would have strong negative feelings about attending the wedding of someone who cheated on them, so it's not surprising that this woman reacted the way she did," she said. 

Moore told Fox News Digital she was concerned that "this woman's sister and family are operating as if her feelings about the engagement and wedding don't matter as much as her sister's 'true love.'" 

Image of Nicole Moore, a blonde woman wearing a blue blazer and glasses, split with an image of two women fighting.

Relationship expert Nicole Moore (left) told Fox News Digital that AlisonVio (not pictured) should speak to her sister and parents separately once she has had time to process the situation. (Getty Images/iStock)

Moore added, "This lack of acknowledgment would make anyone think twice about attending a family event."

While AlisonVio's parents and some of her friends think she should attend her sister's wedding, Reddit users were nearly unanimous in saying that she's right to avoid the occasion. 

"Some friends think I should go to keep the peace and show I'm over it, while others are appalled and say I have every right to be angry."

In the more than 1,200 replies to the post, almost everyone said that AlisonVio is not wrong for not wanting to attend.

"Let's review here. Mike cheated on you and broke your heart (presumably with someone else, since Lily says they started dating after your breakup). Now that very cheater is with your sister and they, including your parents, hid this fact from you," Reddit user "No_Construction_1096" said in one of the top replies to the post. 

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"Now they drop this bomb on you, call you heartless for not believing in their 'true love' and Lily even dares to ask you to be her maid of honor?" wrote the same person.

"If Mike cheated once, he will cheat again. That much I foresee." 

No_Construction_1096 advised AlisonVio to go low-contact or non-contact with her family in the future, "depending on how they decide to behave in future toward you." 

reddit app logo

Reddit users were nearly unanimous in saying that the woman was "NTA" if she decided not to go to her sister's wedding.  (iStock)

Another Reddit user was critical of Lily's decision to date Mike in the first place.

"I just can't imagine ever wanting to date somebody who cheated on my sister. If you break my sibling's heart, you are dead to me. There is no relationship to be had there," said user "readthethings13579."

"Lily’s a bad sister for even entertaining the idea of a date with the man who betrayed her sister, let alone marrying him," the same user added. 

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And one Reddit user had a rather nefarious suggestion for AlisonVio.

"My petty heart was saying, 'Agree to be the [maid of honor], then just give a toast of the romantic history at the reception," Reddit user "KanaydianDragon" said. 

"Bit scorched earth, but who needs a family like this anyway?" the same user added. 

Moving forward, Moore recommended that AlisonVio tell her family that she does not plan on attending the wedding, but "she is going to take some time to emotionally process the event to see if she can come to peace about it."

Afterward, AlisonVio should speak to her sister and her parents separately about the upcoming wedding once she has time to better collect her feelings about it, Moore said. 

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"For instance, the woman might decide to attend the wedding but not be a maid of honor, so it would be easier for her to leave the wedding reception early if it all got to be too much for her," she said.

Fox News Digital reached out to the original poster for comment.