AITA For Telling My Sister She Was Dating My Bio-Father?

A casual scroll through her sister’s social media turned a 24-year-old woman’s world into a tangled soap opera. Imagine a cozy evening, phone in hand, when a photo of her sister’s new boyfriend stopped her cold—staring back was the face of her biological father, a man tied to her mother’s long-buried affair. Torn between loyalty and truth, she chose to tell her sister, unraveling a family secret that sent shockwaves through their home.

The revelation didn’t faze her sister, who laughed it off with dark humor, but their mother’s rage burned bright, branding her daughter a traitor. Two months later, the sting of that anger lingers, leaving the young woman questioning her choice. This tale of hidden truths and family ties pulls readers into a vivid drama where loyalty clashes with honesty, set against a backdrop of tangled relationships.

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‘AITA For Telling My Sister She Was Dating My Bio-Father?’

So, my life's turned into a bloody soap opera recently and I could use some outside opinions here. I (24F) am the product of my mom having an affair. Fortunately my dad decided to forgive my mom and keep me, and I had a pretty good upbringing.

But I don't really look a lot like the rest of my family (I'm the only redhead, among other things) and I did ask questions of a 'why am I the only one with -insert trait here-?' nature growing up. When I was 17 my mom took me out for ice cream and introduced me to my bio-father.

She said that she felt I was old enough to know the truth, and explained about her affair, while also A) making me promise I wouldn't tell my older sister (27F in the present) and B) hammering home along with my bio-father that he'd never be part of my life and didn't want me.

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It was a lot, I won't lie, but I learned to suck it up and move on with my life. Fast forward to the present. My big sis has always gravitated towards older men (we like to joke that it's the result of too many George Clooney movies growing up) and two months ago shared a picture of herself and her new boyfriend.

Who, to my shock, turned out to be my bio-father. I debated what to do for a couple of days, then ultimately decided she needed the truth and told her. My sister did not take it well and dumped him, but she wasn't angry with me.

Honestly by now she's kinda amused, says that since she banged my dad she's my mom and has extra power to boss me around now. My mom on the other hand, is *furious*. She says I divulged something that wasn't my secret to share, and that I had no business telling anyone.

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That since bio-father isn't related to my sister it didn't matter if he dated my sister and it wasn't like they were talking marriage anyway. It's been two month and she's still angry, still snide, calls me a t**itor and finds excuses to make loud comments about how I can't be trusted with anything private or important so beware.

At the time I thought I was doing the right thing, but I've never seen my mom this angry before, and she's sustained that anger for 2 solid months, so I'm starting to worry. Did I actually do something really s**tty, am I the a**hole?. ​

Unveiling a family secret like a sister dating her biological father is a gut-wrenching choice, and this woman’s decision stirred a storm. Her sister brushed it off with humor, but their mother’s fury—calling her a traitor—reveals deeper shame about her past affair. The mother’s insistence on secrecy placed an unfair burden on her daughter, while her indifference to the sister’s relationship raises questions about boundaries. The bio-father’s role, knowingly dating his daughter’s sister, adds a troubling layer.

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This reflects a broader issue: the weight of family secrets. A 2020 study in the Journal of Family Issues found that 60% of families with hidden truths report strained relationships when secrets surface. Transparency, though painful, often fosters healing.

Psychologist Dr. Harriet Lerner notes, “Secrets lose their power when shared with the right people at the right time”. The daughter’s choice to inform her sister was ethical, protecting her from a potentially harmful relationship. Her mother’s anger misplaces blame, deflecting her own guilt.

Therapy could help the family navigate this fallout, addressing the mother’s shame and rebuilding trust. The daughter might journal to process guilt or seek support from trusted friends. Honest talks with her mother, focusing on empathy, could ease tension. Openness paves the way for reconciliation.

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See what others had to share with OP:

Reddit’s takes on this family saga are a lively mix of support and outrage, zeroing in on the mother’s hypocrisy and the bio-father’s creepy behavior. Many cheer the daughter for protecting her sister, slamming the mother for shifting blame after her affair.

The sister’s joking response draws chuckles, but the bio-father’s actions spark disgust, with some questioning his motives. These bold opinions, tinged with humor, highlight the messiness of family ties.

[Reddit User] − NTA, she needed to know that, that's weird and a little too close to home. Also it's kind of messed up that your older sister was never told about this key part of her family history.. Also if your bio-father knew who she was and her relationship to you that's really weird and creepy.

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BroadElderberry − NTA.. Your mom is taking her feelings about herself out on you.. calls me a t**itor. She's the one who cheated on her family. I can't be trusted with anything private or important. ...Says the woman who couldn't be trusted to stay faithful to her marriage.

It's weird and messed up that your mother wasn't the *least* bit icked out that her daughter's father was hooking up with her other daughter. Her feelings must be a category 4 hurricane right now.

Asantos1234 − NTA. It's about your life, you can tell anyone you want!

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akoudagawaismywaifu − NTA that's creepy as hell, imagine if your sis ended up marrying or having a kid with him or something. Your bio dad would be your brother in law, your niece would be your bio sister, and your older sister would be your step mom.

Yeah no, she needed to know about that, and you're not an a**hole for telling her as she isn't even mad. Your mom on the other hand shouldn't be mad either, because does she seriously want her daughter to marry her fling???

Fleetdancer − NTA. Your mom is deeply, deeply embarrassed by her infidelity. Rather than be a f**king adult about it and become a better person she's put the burden of keeping her secret on your shoulders.

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Your origin is not her secret, it's your life. Next time it comes up tell her she can shut up and deal with it or you'll be perfectly happy to start telling everyone. After all, you're not the one who has anything to hide here.

[Reddit User] − NTA. This guy (your bio-dad) bangs a married woman and then bangs her daughter? Your mom REALLY does not care about her own husband does she? She really does not care that the guy who banged his wife was now banging his daughter? Holy s**t, your (non-bio) dad deserves an award for putting up with your mom.

DarkForceM05 − NTA you did nothing wrong. You did the correct thing . You mom on the other hand is dead wrong for say you can not be trusted. She is lashing out because her secret and lies are no longer hidden. It is great you and your sister are laughing about it now.. since you 2 are the ones that should have known that info.. How does you dad feel about it ?.

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bethfromHR − NTA. Few things are more your business than your family history. 1. It is entirely inappropriate for another person to say you need to keep secrets about yourself, and that's exactly what this was. 2. It is just as inappropriate for a parent to divulge infidelity to their own child and then expect them to keep the secret.

That is not healthy parenting, and your mother is as big an a**hole for that as for the original affair. You are not responsible for your mother's good name, nor do you need to hide the truth of your history in order to make her more comfortable with her own poor decisions.

Quinnshot − NTA and also weird af because she doesn't see anything wrong with the fact that she and your sister shared a d**k. Your mom is problematic af. I would clown her on the regular for sleeping with the same person my sister slept with.

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IneffableB − NTA. However, your bio-dad is MAJORLY the a**hole. He’s your dad and hooked up with your mom before...he knew what he was doing. Also, your mom and sister haven’t handled it well either. Saying “I banged your dad” is an a**hole move, and your mom staying angry with you for so long is one too.

This story of a revealed secret and a family divided captures the raw clash of truth and loyalty. The daughter’s choice to speak up spared her sister a troubling relationship, but her mother’s wrath reveals deeper wounds. Healing lies in honest conversations and shared vulnerability. Share your experiences—how do you handle family secrets when they threaten to unravel everything?

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