In a viral Reddit post shared in the Am I The ** group, which can be seen here, user FirmConsideration60 explained her stepmom had been married to her dad since she was seven.

The Reddit user, who is planning her wedding, added they had come together as the result of an affair and that it was something she only discovered when she was in her late teens.

While the woman explained she had a good relationship with her stepmom, that changed following her engagement announcement on social media.

The stepmother then shared a post that the Reddit user considered to be in poor taste that in her mind exposed “she had always planned to have the affair.”

According to private investigation firm LA Intelligence, some 56 percent of men and 34 percent of women who commit infidelity rate their marriages as happy or very happy.

Zoe Burke, a wedding expert and editor of Hitched.co.uk, told Newsweek “there is nothing as stress-inducing when wedding planning as family dynamics.”

The Reddit user then continued: “The post was distasteful and honestly was exposing that she had always planned to have the affair. It did change how I felt. I told her to take it down and apologize, she told me she did not regret the post and why wasn’t I happy she loved me that much.

“I accused her of trying to rub it into my mom’s face that she had stabbed her in the back and won the love of my sister and me after betraying her with our dad like she did. She told me it was 20 years ago and mom should be over it.”

“I decided not to include her in any wedding planning. She is a wedding planner as a profession and I know she would want to, but I am not happy with her post. Mom was so happy when I told her.

“But when my stepmom wanted to know when she’d be dress shopping with me and what I wanted her help with, I told her I did not want her involved in any wedding planning.”

The Reddit user added: “She and my dad are saying I am overreacting and should not be treating her this way when she has been a damn good parent to me.”

Burke told Newsweek there are several things to consider when planning a wedding and how best to approach sensitive issues in the family.

She added: “When you are planning your wedding, you reserve the right to do it however you want, and with the help of whoever you want. If that’s just with your mother, then that’s fine: no one has a ‘right’ to be involved with the wedding planning if you don’t want them to be.

“The best thing to do—which it seems like this bride-to-be has already done—is to be calm and honest when you explain your plans and your reasoning behind them. I can speak from personal experience here, as a step-parent, you do become accustomed to taking a backseat and following the lead of the children when it comes to how they want to structure dynamics with their parents.

“The stepmother in this instance should understand that the bride wants to share this experience with her mum, and that she needs to step back and allow that to happen. If the stepmother truly loves the bride-to-be then she will understand that, and put her wants and needs first.

“I would always recommend a calm and honest conversation about your plans and wishes, and if you can, offer a token role in the wedding or duty within the planning to allow them to feel involved in some way, but this is only if it works for you.

“Ultimately, at your wedding, which you’re paying for and planning, you have the right to run it exactly how you want to.”

Since being shared on November 8, the post has attracted 9,200 upvotes and more than 1,000 comments.

The overwhelming majority of commenters praised the bride-to-be’s decision and gave a frank assessment of what they thought of the stepmother’s behavior.

Reddit user thetaleofzeph, whose comment was upvoted more than 1,800 times, said: “She’s peeing at the corners of what she thinks is her property.”

Commenter EmeraldBlueZen posted: “Her minimizing the pain your mom must have felt, that she needed to get over it because it’s been 20 years, is absolutely infuriating.”

Newsweek has contacted FirmConsideration60 for comment.