Always a Gran

paddyann after OP has been married for 15 years I would consider her DH as family but we all have our own thoughts on what constitutes "family"

sarahellenwhitney my feeling exactly, my DD would have invited my DH rather than her F to events. It seems strange to me that although you have kept asking about arrangements for DGD's 18th your DD only tells you at the last minute that you're invited, on your own on a Friday night. I would feel very hurt but then I was never excluded from any celebrations for DH's family or him from my own family events.

OMG this man has been part of the family since the granddaughter was 3y old! Likely she will have NO memories whatsoever of her biological grandfather. He’s been grandmother’s partner/husband for 15y! Sounds more like the adult daughter (mother of the 18y old birthday girl) has issues here. Hmm.

He is outside the family, why would he be invited to a private family party?

Please listen to wise voices who say exalt that you were included in their tight family circle of just parents and children. You must be very special and if it were me wild horses couldn't stop me donning my best and celebrating with your special 'girl'. Slap on a big smile and enjoy yourself twice - this time and at next party with dh. Your comment about your daughter never calls just emails gives me a little insight that maybe you are hurt and harbouring a little resentment and this seems to have inflamed your reaction to this? I married again but my husband much as I love him knows and understands the unbreakable bond with my children, who after all I've known longer than him! Don't make it 'him' or 'them' choice. You will regret not going . Let us know what happens.

They have tried, perhaps clumsily,to be diplomatic by inviting you both to an event later. There are some family occasions when the people we love just want, maybe for one evening, to have the people they love most around them. Those are very precious times, not easy to explain to others who they might also love in a less intense way. We recently had an evening meal with our son and daughter( at my daughter's request) She lives in a different part of the country. Now we adore our SIL and DIL and also our grandchildren and would not hurt them for the world but what are the chances of us seeing our own little nuclear family and just being the four of us in our lifetime? I think it has happened two or three times in the past 30 years. It was a wonderful evening and one that I will treasure for ever. I think we all felt the same. It does not infer a lack of love or respect for any of the others in our lives.

I second that. Today I spent time with my son and grandson. No DIL, no DH(= stepfather). It was a lovely opportunity, not to be missed.
I hope the OP can view this event in the same way.

If in doubt act with understanding and love - its our 'dramas' which cause our pain and here is a wonderful opportunity to just be simple, and not look for meanings which are probably not there at all. You are wanted by your DGD and your DD - what a wonderful gift, which others would love to have. I am sure you love them and they love you - I hope you go and enjoy celebrating with them, and no lingering doubts.

Like you, I would feel extremely hurt as I would see it as something deeper, like questioning your choice of DP. So I would try to find out the reasoning behind this decision, after all, as Urmstongran says, your DGD has only memories of this GF. If she doesn't want him there, or more likely your DD, there are issues to resolve. If it's a question of expense then that's fine, or you could offer to pay 'for her birthday'. In any case I'd go anyway, and paste on a smile, but wouldn't be happy about the snub to my DP.

Tell her you’ve cancelled your previous arrangements and are happy to join in the celebration. Don’t pay any attention to those on herewho are fuelling your hurt by their own angst.

This thread has been a right niggle in my mind and I’d like to know how it turns out.
For me OP has 2 options.
Take umbrage and not go. Thereby missing out on a lovely evening and being the one who spoilt it.

Or, be happy that you were included and celebrate with a precious grand daughter on her very special day.

Lots of Grans on here who don’t have any relationship with their GC through no fault of their own.

I know which option I’d choose. In fact option 1 would never enter my head.