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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

How to deal with this situation? BIL & his kids as a result of an affair?

299 replies

jojobooh · 20/11/2025 14:41

Basically my BIL had an affair behind his long term partners back (has a son (10) & a daughter (14) with her) which resulted in twins being born who are now 5.

The kids have never met and are not aware of the existence of each other because of several reasons.

We have DC who are closer in age with the twins and have play dates often.
Our oldest DC talks and understands and is very cleaver.

DC see both lots of cousins, obviously separately and are aware that they are cousins and family etc.

Were having a Christmas party for all the kids in the family next month in our home, just abit of festive fun for the kids.

Now as the kids are not allowed to meet each other BIL wants us to host the party twice to neither of the kids miss out.
I think this is absurd.

Whilst we want all the kids to be treated fairly and equally I find this request unfair and OH is supporting BIL.

Why should we have two parties?

Moving forward I think this will be a similar trend when DC have birthday parties etc or other future family events we host.

And when DC are older they will be forced to keep this secret which I don't think is fair or right at all to swear young kids to secrecy.

I just wanted to see if I was BU about refusing to host this second party and if anyone else has been in a similar situation.

OP posts:
HappyHedgehog247 · 20/11/2025 16:47

The children will all feel betrayed that their father has lied to them by omission. You cannot ask your children to keep a powerful family secret and it sounds like they are coming to or at the age where this would be required. The party is just the catalyst that has brought this to a head. Family secrets do long term damage to relationships.

Hankunamatata · 20/11/2025 16:47

The poor 10 and 14 year old. A whole secret family they know nothing about

Does bil even realise the longer he leaves this the less chance kids will forgive him

Howwilliknow122 · 20/11/2025 16:49

reversingdumptruckwithnotyreson · 20/11/2025 16:40

Frankly I wouldn’t have had my children involved in this lie to begin with, so I’m not sure what to say on that front. The whole situation is horrible.

My ex-SIL had a half-sister born the same year as herself, they even ended up attending the same university but simply never acknowledged each other. But at least they were aware of each other’s existence.

Exactly. Well said. Ops biggest issue here is her inconvenience of having to throw two parties... mean while these kids are all being lied to.. oh but ops kids are very smart dont forget 🤦🏻‍♀️

Millytante · 20/11/2025 16:49

jojobooh · 20/11/2025 15:16

BIL split up from his ex and is now in a casual sexual relationship with the twins mum.
The kids all live with their mothers but he does a lot of school drop offs/ pick ups and is active in all of his kids lives.

Except for the fact that he is still lying to his original family.
I would make every effort to keep such a man out of my own family’s midst.
(The behaviour of the affair woman was dreadful and borderline flaky, and I’d not want her nor their twins around under present circs, either.)

This leaves the older kids, and it’s they and their mother who have been your family from the start, and until BIL regularises the ghastly situation, I’d carry on regarding this trio as my in-laws and cousins, but no others.

BIL is not acknowledging his affair kids, and it’s grotesque of him to expect your children to accept them as cousins but pretend, through LIES, that they do not exist.
He and his younger kids wouldn’t be welcome anywhere near my house with that nonsense going on.
If he just wants the kids to be happy and to attend family parties, he knows what he has to do, and it’s not up to you to make up for his lack of a backbone.
Still less is it up to young cousins, ‘clever’ or not, to play a part in this appalling deception.
Nobody should expect children to lie to cover up an adult’s crimes and misdemeanours.

A second party? Feck orf! He should have thought of complications like this when he was happily impregnating another woman. The rat.

Millytante · 20/11/2025 16:50

Howwilliknow122 · 20/11/2025 16:46

Op im shocked you think its ok for your kids to have a relationship with the twins when their actual half siblings are none the wiser. You're worried about hosting two parties? is that your biggest issue, what will all these kids think when they grow up and find out you've all been lying.

Edited

Well said. OP has everything upside down.

IggyAce · 20/11/2025 16:51

This has to be one of the most fucked up things I’ve read in a long time. Those kids deserve to know and are going to need years of therapy and will have massive trust issue for life.
Honestly my kids would be no part of it, it’s wrong to expect children to lie.

Charlize43 · 20/11/2025 16:51

What would Nancy do? Oh yes...

How to deal with this situation? BIL & his kids as a result of an affair?
BellesAndGraces · 20/11/2025 16:53

jojobooh · 20/11/2025 16:35

Apparently the partner he cheated on dosent want her kids to meet the twins either, I'm not really sure of the reasons.

She is understandably very angry and bitter about the whole situation and how she found out (the woman called her up out of the blue to ask when the kids were meeting).

It is very messy and BIL does need to put things right and be honest.
OH defends him to the core so it's hard to enforce/ say anything in relation to this.

OH's reasoning is "because the ex is an alcoholic my brother had the right to do what he wanted and it's her fault for making him so unhappy".

When I reason that most normal men would leave the relationship and have the courtesy and respect to tell the woman how he felt/end the relationship before getting someone else pregnant, he starts getting nasty and blaming the ex.

Your DH is telling you exactly how he will behaviour if he becomes unhappy with your marriage …

Itworkedout · 20/11/2025 16:56

I would have said no to involving my children in his secret family, he needed to come clean then to his children. They will hate him more for lying. He didn’t think this through did he. He has involved your children and at some point someone is going to spill the beans. His older children aren’t going to thank you for it either. I think you need to stand up to him and definitely not two parties!

themerchentofvenus · 20/11/2025 16:58

jojobooh · 20/11/2025 16:19

The oldest two kids are early 20s (BIL was 17 when he became a dad).
They didn't see their dad for years and the kids lived with their mum and grandparents.

BIL came back into their lives when they were 12 and 13.
They have serious daddy issues.

They have been involved in stabbings, drugs and one is currently incarcerated for a stabbing.
BIL used to go clubbing with them and allow them
to smoke marijuana.

The 10 and 14 year old's have witnessed domestic abuse, their mom is an alcoholic which is apparently one of the reasons why BIL had an affair apparently.

It is very unfair on the kids.

I have tried to approach this with OH but he gets nasty and very defensive of his brother.

So the oldest two are criminals, the middle two have an alcoholic mum, and the youngest two have a stalker mother?

That is one very f*cked up situation. All those poor kids.

Your kids should NOT be part of this or expected to lie. Two Christmas parties are ridiculous.

The middle two need to be told about their (other) half siblings, as otherwise this is going to really mess them up. He might be afraid they'll hate him, but they'll hate him even more if he doesn't tell them.

MrsBennetsPoorNervesAreBack · 20/11/2025 16:58

jojobooh · 20/11/2025 16:35

Apparently the partner he cheated on dosent want her kids to meet the twins either, I'm not really sure of the reasons.

She is understandably very angry and bitter about the whole situation and how she found out (the woman called her up out of the blue to ask when the kids were meeting).

It is very messy and BIL does need to put things right and be honest.
OH defends him to the core so it's hard to enforce/ say anything in relation to this.

OH's reasoning is "because the ex is an alcoholic my brother had the right to do what he wanted and it's her fault for making him so unhappy".

When I reason that most normal men would leave the relationship and have the courtesy and respect to tell the woman how he felt/end the relationship before getting someone else pregnant, he starts getting nasty and blaming the ex.

Tbh, none of that is really relevant.

The priority for you and your H should be to protect your own children. You don't have to make judgements about any of the adults involved, you just have to do what is right for your kids.

And sooner or later, one of them will let something slip, and they will get the blame for upsetting their cousins. Are you really going to stand by and let that happen?

Just grow a backbone and insist that you and your children will not be playing any part in the deception.

Millytante · 20/11/2025 17:00

jojobooh · 20/11/2025 15:36

OH did try and tell me when the twins were born.
He made a joke "BIL has quite a football team now" and I said "What do you mean?"

He said BIL had twins with another woman and by my reaction (horrified, disgusted and angry on his partner's behalf) he told me he was joking and it was a prank.

I thought nothing of it as nobody in the family mentioned anything but I did keep asking him why he said it and it came out of nowhere.

As PP points out I am worried about the kind of message it will teach my own kids.

Well, you yourself aren’t as steadfast about honesty as one might wish either, if you'd ever dream of letting your children engage in the cruel lying BIL is demanding.

Namechange29383929383 · 20/11/2025 17:02

So he has six children in total, oldest two know they’ve got four younger siblings, middle two only know they’ve got two older siblings, and youngest two don’t know about any of the others? And then you’ve got your primary age kids in the middle who hang out with the younger two kids and have to pretend they don’t exist when they see the middle two? What!?!

This is BILs mess to sort out. Don’t host a second party and don’t put pressure on your kids to keep the secrets of adults. In ten years time your kids won’t be little anymore and if that’s when it all comes out they’ll be the ones unfairly shunned by both sets of siblings for not saying anything earlier.

WilfredsPies · 20/11/2025 17:09

jojobooh · 20/11/2025 15:36

OH did try and tell me when the twins were born.
He made a joke "BIL has quite a football team now" and I said "What do you mean?"

He said BIL had twins with another woman and by my reaction (horrified, disgusted and angry on his partner's behalf) he told me he was joking and it was a prank.

I thought nothing of it as nobody in the family mentioned anything but I did keep asking him why he said it and it came out of nowhere.

As PP points out I am worried about the kind of message it will teach my own kids.

Wow, sounds like the two brothers are birds of a feather. What did he say about lying to you when it all came out?

It’s only a matter of time until the children find out; probably from one of your children. Because that’s what children do. They talk. And the longer it goes on for, the more likely they’ll be to turn out like his elder two children. Utterly fucked up because of their failure of a father.

My concerns would be that your DH doesn’t get aggrieved with any of your DC if/when they disclose the existence to one or both sets of cousins. I’d be making it very clear to your DH that if he or any of his family so much as looks sideways at them because they didn’t keep this grubby little secret, there will be life changing consequences.

As far as the party goes, I’d refuse to have any part of it. I’d tell BiL that you’re only hosting one party and the rest is his problem to solve. If DH disagrees, then DH can throw a second party without any involvement from you. I’d also be making it very clear that you won’t lie to any of the children and if they ever ask you, then you will tell them.

thestudio · 20/11/2025 17:10

I'd also watch your own DH if I were you - his moral compass regarding infidelity is utterly fucked.

Sassylovesbooks · 20/11/2025 17:13

Quite honestly your BIL is a shit bag for not only cheating, that resulted in twins but equally for putting his entire family in this utterly ridiculous position. It doesn't matter what his justification is, at some point his middle children will find out of the existence of his twins. All your BIL's family are enabling his behaviour, by not all sticking together, and telling him to get his shit together. The betrayal his middle children will feel, when they realise every adult in their family has covered up this charade is going to be immense. He's purely thinking of himself, and his ex is bitter/angry and thinking of herself too. How about he and his ex put the children first, and think about how devastated they be when they eventually do find out. This is all on your BIL, for not keeping his dick in his pants, until he'd left his ex. You clearly aren't going to get anywhere with your husband, because he's defending his brother and the choices he's made. I would tell him, if he wants to host two parties, then to go ahead, but you won't be enabling this any longer. Tell him bluntly that you don't agree with the set up any longer, it's not fair on your own children to be expected to keep 'secrets' and when the shit hits the fan (which it will), you aren't getting involved.

WearyAuldWumman · 20/11/2025 17:16

@jojobooh Tell him to get stuffed.

A close family member discovered when he was 24 that he'd been adopted by kin. (His 'Dad' was a blood relative; his 'Mum' wasn't.)

Both his birth family and his adoptive family on his stepmother's side went to elaborate lengths to stop the siblings from meeting. My family member was in his 60s before he met his siblings.

He forgave the siblings and younger cousins involved, but could never forgive the adults who enabled this - even to the extent that when my family member's cousins visited from abroad (as adults) - his adoptive cousins were told by their parents "Don't mention X."

WearyAuldWumman · 20/11/2025 17:16

@Sassylovesbooks

Well said.

Arlanymor · 20/11/2025 17:18

All these adults thinking about themselves and not the children who are the innocents in all this. It's horrific, truly it is.

Well if your husband is lacking a moral compass then no point trying to get him to magically grow a spine. In which case you just need to make it abundantly clear that your children will no longer be seeing the 'secret twins' until such time as they are no longer a secret, because you don't want them to ever be in a position where they have to lie, or where they get blamed for this whole deception. So it stops now. No more parties, playdates or anything else. If either your BIL or your husband kicks up a fuss then just say: "Well you know how this can all be solved... you tell the middle children the truth."

frostedpixie · 20/11/2025 17:19

His older children deserve to know about the existence of their half siblings.
Their young cousin has a relationship with these kids ffs but they've to be kept in the dark? It's disgusting.

You're all complicit in the mess he made. You need to give yourselves a damn good shake.

Scottishskifun · 20/11/2025 17:21

No way would I be hosting 2 parties for BIL cover up.

It's a simple I'm not hosting, paying and tidying up.
Either BIL can host one at his house and one at the twins mums house or both at his.

I also would be clear with your DP you will not be telling your children to lie so if they say about cousins in the future then your not going to stop them.
My 6 year old often talks about family so that's likely to be sooner rather then later with yours!

Arlanymor · 20/11/2025 17:22

WearyAuldWumman · 20/11/2025 17:16

@jojobooh Tell him to get stuffed.

A close family member discovered when he was 24 that he'd been adopted by kin. (His 'Dad' was a blood relative; his 'Mum' wasn't.)

Both his birth family and his adoptive family on his stepmother's side went to elaborate lengths to stop the siblings from meeting. My family member was in his 60s before he met his siblings.

He forgave the siblings and younger cousins involved, but could never forgive the adults who enabled this - even to the extent that when my family member's cousins visited from abroad (as adults) - his adoptive cousins were told by their parents "Don't mention X."

That's so sad - in his 60s - they stole time from him, they stole his sense of identity, they stole his opportunity to build closer links with loved ones.

It stinks, it really does.

WearyAuldWumman · 20/11/2025 17:22

I'll add that - in my experience - the repercussions of this kind of subterfuge can extend beyond death.

Homegrownberries · 20/11/2025 17:22

Op, you have to seriously question what sort of ethics are being modeled to your own children. You're teaching them to lie and deceive. Your husband is teaching them that it's ok to turn nasty when challenged and that the woman is to blame no matter how a man behaves. If you don't break the cycle the next generation will just carry on with more of the same.

SheilaFentiman · 20/11/2025 17:23

Why on earth does your OH think it’s relevant who was to “blame” for BIL’s affair? The consequence was a pregnancy and two half siblings that have been kept a secret.

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