Always a Gran

I think you should go, accept your partner isn’t your granddaughter’s grandparent, but he is welcome at the bigger celebration later.
I think it would be dreadful to miss her actual birthday, and all because you feel miffed. She’s your grandchild, go!

You say, what’s so special about you? Well, what’s special is that you are your daughter’s mother, and granddaughter’s grandmother. That’s a special and wonderful relationship, do not let them down, there are many grandparents on here who never see their grandchildren. You must go.

DH's brother's wife didn't take to me though hadn't had time to get to know me either, and didn't want me to come to the funeral. The feeling in his family was that our marriage would not last.( It did for over thirty happy years till I was widowed .)
I didn't know you could just go along Mrs Eggy so thanks for that information.

I'd be honoured to be invited to such a small family gathering, and over the moon that DGD wanted me there. Don't let her down.

I think it is sad that you are putting your husband first. Children don't have to accept step-parents but they obviously do as he is welcome to the later event. Would he not accept this?
Sorry, but people should be able to see a parent on their own and I cannot see you as being in the right here. It just seems like stubbornness. Even if they were being unfair, it is a day to put your grand-daughter first.

The original post does not mention anyone other than her daughter and granddaughter being present and if that is so then it is entirely reasonable for OH not to be included, a girls get together with a meal, i would feel privileged. However, if anyone else is going and sil and granddaughter's boyfriend etc then you probably have cause to be resentful. However, I never foisted my other half on my sons as they did not like him so he visited his kids and I visited mine which was a reasonable compromise. My kids will always come before a man who is not their father but as I am now single it is not a problem.

Why must you ask why he is being left out? You have both been invited to the main celebration.
I would just go & enjoy it. If I were your DH I wouldn't feel at all miffed.

Just go. I would.

Speak to your daughter, tell her you'll happily change your plans but wonder why no invite for DH and why such a late invite after you've been asking for details re celebration for a while now. I think you have to go for GD's sake and hope the explanation for DH's non -invite makes him feel better about being 'excluded'.

Go

I agree with Madgran.
It seems rude to me to invite only one of a pair, unless it’s a gender-specific ‘do’ such as a pre-wedding hen or stag.
So I’d accept the invitation for the sake of the gd but would politely and reasonably ask why OH wasn’t invited. If it’s ‘close family only’ it’s sends a message that he’s not accepted as family, which is sad for future family events.
Are other married-in partners also excluded?

I must say I look at this rather differently. To me it is an enormous piece of cheek to expect anyone to want to go to a function that they have expressly been asked not to bring their spouse to!

You live with your husband, not with your granddaughter. Shame for her that her parents have no manners, unless of course, there is a good reason for them not wanting your OH there, but as you will both be going to the later celebration, I would let granddaughter do without me at the small party, if I were you,

Seems to me every family has some strange family dynamics. If you have already emailed your daughter back and said no, say you had a change of heart and go. It sounds like your daughter does not actually have an issue with your husband if she is inviting him him to the 2nd event.
And I would just happily assume it's not cost but that your grand daughter just wants her parents and you at this dinner. And that's OK and maybe that's also why your daughter was so slow with the invite is because maybe she knew it might hurt your feelings.
Lots of guessing on my part but the fact that he is invited to the 2nd larger event might mean they like him but that your grand daughter may be missing her real Grandfather on her birthday.
So please go it's her birthday and it is her day so let her have it however she wants it with no ill feelings.

I think you have done the right thing. Why would they not want to invite your OH after 15 years? Your GD has known him for almost all of her life and assuming there are no other family issues of course he should accompany you or you don't go.
By all means ask why they wish to exclude him, but it does not sound reasonable based on what you have said.

It does seem a bit mean to exclude him. he must have known her since she was 3.
I don't know how long ago her "real" grandfather died but she can't have many more memories of him that she does of your husband.

If and when she marries, I am sure you will always include her husband in any invitations.

We are sort of assuming the wider family thinks there is something wrong with OP's partner but it could be that there is another person who they don't want to invite so they are saying "family" only. Like couples who don't want particular children at their wedding so find the only way to avoid causing offence is to ban all children.
Surely straight forward communication without recrimination is the answer. I would put my GD first on this occasion and my DH would accept that even though we tend to think of my GD as his and vice versa. My DH's thoughts would probably be along the lines of a/ whatever kept me happy and b/ it was a lucky escape for him

My DH would be delighted not to be invited, in similar circumstances. We often visit our own families separately. We go together for a really big occasion, but not generally.

The OP has the chance of a close family event, which I would jump at, and also a bigger do, including her DH. Best of both worlds.

Speaking from personal experience, sometimes it is hard if you just want your Mum and not her partner at a small family gathering, it doesn't mean you are being horrid, it just means that you want your Mum to yourself for a bit. Treat that as a compliment rather than a swipe. Your partner is invited to the bigger celebration later, just feel lucky that daughter and Grandaughter want you on your own for a bit. I feel like this about My own Mum, partner gets invited to most things, but just sometimes you want your own little unit with shared memories etc.
Just my ten pennorth !!

I think that icanhandthemback has made a very good point.

The people that they want at this meal are the very closest _blood- relatives of the birthday girl.
By extending this to include a non-blood relative, albeit Grandma's DH, they increase the likelihood of upsetting other blood relatives, who might be upset they haven't been invited too.

Given that there is to be a big celebration for everyone, at which he is welcome, is it really that big a deal?

I'm afraid I would be going to my granddaughter's 18th. Could you ask your daughter why your husband isn't invited. If they are paying for the meal, maybe they just want to keep it for a few people, especially if there is another celebration?

I really think you should put your pride (and your negative thoughts) in your pocket and celebrate your GD's 18th with her and her parents. If you don't there won't be a second chance.

Your daughter will have a vision of what it is all about and I guess she would be clear that she has no intention of upsetting you or your husband - as is shown by his being invited to the later event. She would probably be amazed at your interpretation of the invitation, and the risk is that you create some family friction here, without meaning to. Friction which was never there from your daughter's side. Your granddaughter would miss you being there and will only have one 18th birthday! So I agree with others - go and enjoy the event! Let go any lingering story about all this - we can never be sure of someone else's thoughts and you could give the benefit of any doubt to your daughter and have a lovely time together.

I’d take it as a compliment that they want you all to themselves for this one special night. I often see people without their other halves, not because I have a problem with them, but the chat and the atmosphere is different when it’s not a couple.
It’s a shame you can’t see the joy in being included in a special group of people that love you.

Nanny41.
Were it me I would feel hurt that my daughter could not bring herself to include OH in this event. Does she not get on with her stepfather? are you not entitled to have a life after her own father.
Put yourself in his position. How would you feel.?Can you not ask DD why she does not want OH there?

he's not her dad or the grandfather so why would he be included in a "family" event ?