Yes–oh, very, very much!
Does the half sister know about any of this? I think her feelings should be taken into consideration as well, but if she’s not aware of the situation and hasn’t been contacted by the OP then that may not be possible.
If this discovery was made through genealogical DNA testing, it probably would have been best to ask how people in the family would feel about this sort of thing before you got the results. It’s too late for that, but in this situation (if you think you could pull it off) then I don’t think it would be wrong to tell a white lie and act like you didn’t have the results yet and ask whether the cousins would want to be told anything surprising about their family history that came to light.
If you had asked 10 years ago, when both parents were alive, no. My parents had a wonderful marriage, and to learn Dad had fooled around…just no.
Now, yes, I’d want to know. I have 2 siblings, one a brother who I consider worthless, and the other a sister who lives over 2000 miles away. She is…um, let’s say “discouraged” from spending time with me. 
I find myself without family. I hate it. I’ve cried every holiday since we lost Mom. Aaaannd today is Mother’s day. (I will not think about it…I will not.)
davida03801, since you know the family, you’re the one to answer the question. If the parents were happy, and the thought of Dad running around would offend them horribly, maybe you don’t want to tell them.
After reading all the answers we’ve given you, run the “if this, then that” through your head, and see how it works out. Keep us posted, I for one am curious as to what you decide, and if you do tell; how it goes. I can live vicariously through your drama!
Been there, twice. I was adopted (in-family: birth mom is a much younger sister to raised-me-mom). I didn’t know I was adopted until I was in my teens, and was told birth-mom likely had other kids, but wasn’t positive. When the sisters reconciled a few years later, I met all four of my (younger) half siblings at age 20. The whole bunch moved into the area, and we became pretty close. Fast forward another 8 years or so, and birth mom reconnected with birth dad on Facebook. He also has three children. I chatted with him a few times, but it was kind if awkward and I was kind of over it. His wife was beyond pushy about me “building a relationship with my brothers and sister”. No. But I’m glad I know about them all, and I’m glad I built the relationships with the ones that I did, because I had the choice.
To make sure we all understand how the DNA testing works: this isn’t about someone and their suspected cousin doing a one-to-one comparison test. When you do autosomal DNA testing you only submit your own sample. It’s analysed and you get results that roughly trace your DNA origins to various parts of the world. You then go into a database. As other people are tested, they go into the database. If you share segments of DNA, then the system shows you your connection and the estimated relationship between you based on the size of the matching segment/s. You can go into this testing with no concept that an secret cousin/sibling/biological father exists and no intention to search for such a person.
Did I discuss the potential ramifications of DNA testing with all my kin before I did it? No. I’m not shutting down an exciting avenue of family history research because someone else might be sitting on a dirty little secret. If you are afraid of skeletons in the closet, you should never take up genealogy. Is it worth foregoing DNA testing because a sibling, first cousin or second cousin might have a love child and create an awkward social situation? I don’t think so. The genealogist did not do the wrong thing by testing, even if testing exposed someone else’s decades-old deception.
The reunions that come out of DNA testing can be positive for all involved - ask me, I had one this very week! It’s not all trauma and lies and broken hearts - no more than any other part of genealogy. This is part of genealogy, and you have a responsibility to others when you start digging around in the past: behave ethically and respectfully toward others, be sure of your sources, do not knowingly or negligently distribute inaccurate information.
I personally would withhold the information from public distribution if it was distressing to close, living relatives, but I would accurately document it in my files, and I wouldn’t actively distribute false information about it, ie I might just list the acknowledged children of the parent and leave off the secret one, but I would never include a field that says Children: 3 if I knew they had four.
No. This happened to me last year, found out after my father died he sired several other children. I have no interest in knowing them or anything about them.
Yeah. I’ve always suspected that my father had another child. There’s been some evidence. A mysterious photo and fathers day card. It’s either a girl about a year older than I am, or a child about 20 years younger.
The photo is either his daughter/grandchild or his girlfriend/child. He died about four months after I found the fathers day card, and there was a mysterious lady at the funeral. His coworkers thought she was family, and the family thought she was a coworker. I lost the address a long time ago when I moved. No one ever sued the estate for inheritance/child support. However, just before he died he told me his finances had changed enough to need to file bankruptcy. No cut in work hours, no new bills, so I’d guess child support.
I’ve been meaning to go to the Social Security office and see if anyone is collecting on his benefits.
I’m not worried about any lawsuits for any insurance money. I was the only one listed on his life insurance, and my lawyer told me that was my money, and I didn’t have to share it with my siblings if I didn’t want to. I did share it. We split it three ways.
The DNA website 23and me.
I joined to discover my DNA makeup as I was curious, then all these DNA relatives popped up. Must have 300-350 of them, if not more.
All of them are probable. As in probable 3rd to 5th cousin, probable 5th to 8th cousin, etc.
That is all except one. This one says “Second Cousin” and it has by far the highest % of shared DNA. So I started talking to this person via email and over 5 months or so figured it all out.
Yes, yes, of course. I am in conversation with her via email. She asks that I be discreet and low key and to make it very clear she does not want to barge in. If they do not want any communication with her, so be it. However she would like to know some about her birth father as she has gone through all of her life never knowing who he was.
I have two half brothers, and didn’t find out they were so until I was fourteen. They’re assholes. Knowing has done me no good - they wouldn’t even tell me how our mutual mom died, no genetic history, nothing. Fuck them and the horse they rode in on. If there was anyone else I wouldn’t want to know either. I like being an only child.
I have a half-sibling who most likely doesn’t know about me.
My parents were unmarried high school sweethearts, I was born in the early 60’s. My mother’s parents were jerks, and made sure my father was not allowed in my and my mom’s life. We reconnected in 2011, and he told me that he had gotten later gotten married, had a kid, the marriage didn’t work out and she left with the kid. (Dad was not the most stable of people, he had problems with substance abuse, but he has a good heart.) He is not in touch with my brother, but he knows the now-grown brother lives in or near one of the Carolinas and has a child.
I have toyed with the idea of trying to contact my half brother, if only to pass along family health information, but I’ve got my own more pressing problems to deal with, so I haven’t pursued it aside from fruitless Facebook and LinkedIn searches (dude has a fairly common name so no luck there).
I would want to know that this person exists, but I’m not sure I’d want to meet them. However, if they initiated a meeting, I would probably go along with it.
Story time!
My parents divorced when I was three years old. I rarely saw my father- maybe a handful of times. He had two sons from a previous marriage, and I vaguely remember meeting them when I was about five years old- they were at least seven years older than me. This was back in Texas. Never saw them, or heard from them, again.
Well, decades later, I moved out of Texas… to a small-ish town in Oregon. I lived there for about four years, and then moved to Seattle. A few months after that, I got an email from one of them- he’d been searching to see if he could get our family name domain, and had found my website. It turns out he lives in… that same small town in Oregon. We’d lived in the same town for four years, halfway across the country from where we both grew up. He runs a construction company, and I remember at one point pulling up next to one of his trucks (and commenting on it to my wife, because my last name has a pretty rare spelling).
We’re now Facebook friends, but still haven’t met in person. Nice guy, though.
I wouldn’t know if I wanted to be told unless I knew, in which case I would already have been told, so I wouldn’t need to be told. Er, again.
I think I might be a little nervous allowing a relative access to my family. Not all people are a good mix.
This. For the first face to face I’d want him/her to be in restraints. (Padded)
A fairly emphatic, NO.
We’d be worlds apart at this age. They’d have their life and I’d have mine. I don’t want those kinds of changes/risks in my life right now.
That being said, I’d not be an ass if they rang up and wanted to meet me. But I don’t think I’d let it go very far (unless she was hot!). 
Oh, I am this person: the mystery half-sibling. I’ve known I was adopted since I was four. Figured out who my bio-mom was a few years ago and finally reached out to her last fall, mainly for any medical info she might have. Come to find out, I have two-half brothers, neither of whom knew that my bio-mom had put a baby up for adoption.
The first time we met face-to-face, Bio-mom brought one of my half-brothers along. He and I hit it off right away, and whenever he’s in my part of the country (twice so far), we meet up and hang out. My other half-brother lives in my immediate area and despite (I suspect) bio-mom’s urging, hasn’t wanted to meet. I totally sympathize. He didn’t ask for this situation, probably never wanted a half-sister, so why should he be lumbered with me now? I hope for his sake that bio-mom doesn’t push him too hard about it. I’m open to meeting him if he ever wants to, but I definitely do not want to make his life more difficult.
What if you meet this person and they immediately start hitting you up for money?
I didn’t say anything about foregoing the testing. I suggested having the “Would you want to know…” discussion before doing the testing so if anything surprising does turn up you know who’d want to be told and who’d prefer to be kept in the dark.