Introducing the new stepgrandpa

He's not your GC's granpa ,hes their granny's husband thats quite different .Its entirely up to your children for now what they decide he'll be called but as they already have a grandpa it may well not be that

No, the grandpa or grandad is his parent's father.

Why not just call him by his forename eg John, Mike or whatever it is?

Talk to your son and dil.

My Nan's husband was 'Uncle Dave'.

If you are the grandma your DH is the grandpa. Simple.

Introduce him with the forename. Leave Grandpa out of it

Just use his first name.
My grandchildren have about 12 adults of grandparent generation in their lives, thanks to various divorces, deaths and remarriages, and they have always known exactly who is who. I am Granny and the number one, and my husband is Grandad, though he is a step. Then there is Grandma and Grandpa, Nanny and Pop, who live further away. The rest are known by their first names and they are partners of step grandparents, or parents of step parents.
They are not confused, they know which ones are important in their lives, and are polite to the others when they meet. It makes for lots of Christmas presents !

I'm with Starlady & sodapop on this one just use your new husbands name he is not blood related in anyway.
My DGSs partner has 3 x step fathers from her mothers marriages the children must be so confused.

My grandchildren and then great grandchildren called my ex, their biological grandfather, Granfer, and my husband Grandpa - no problem.

My GC has 3 grandads. Took them years to work it out, but they have never known any different. I really would not make a big deal out of it, maybe your should just call your husband by his name. Maybe if they just come around for tea and cake and take it really casually.

I would not make a song and dance about it as they say.
Keep it low key, perhaps pick you up from a family visit with the gc. Introduce by name, children will ask any questions they want answering, just answer simply and honestly!

Don't expect too much too soon, and eventually they will become friends I'm sure.

Grandpa---( Christian name )
I have step-families and I'm known as, and called Nan--( Christian name ) by all.

I agree, simple is best. He won’t care at the moment, he’s too young.

Too many abbreviations for me.!!

Just use your new husband's forename Hope23 don't make a big issue out of this.

Oh, I just realized, DS and DIL may be concerned about what to say if GS asks who DH is. IMO, you/they would need to be honest and tell him this is your/Grandma's new husband. But I wouldn't make too much of it, maybe distract him to something else.

"They don't know what steps to take to introduce him to my grandson. Any ideas?"

Why do they feel they need to take any special steps? How do they introduce any new person into GS' life? I suspect they're feeling cautious b/c of how abruptly you left your X and how wrong they were about the state of your marriage. My guess is they don't want GS to get all involved w/ a new person, just to have him "disappear" (b/c this one isn't his actual GF) or to have to introduce him to someone else in a couple of years, etc. I'm sorry if that sounds insensitive or offensive. I'm NOT suggesting that will happen, just that they may be a little wary. I would just introduce him by his first name, and leave it at that for now. The important thing, IMO, is, as others have said, not to try to force a relationship between him and your new DH.

My grandchildren have a stepgrandad. You could do as they do and introduce your new partner as Grandad Fred for example.

This got buried so I thought I’d bump it up

I assume that your Grandson knows your ex as his grandfather?

I guess you introduce him by his name, as he isn’t related to your Grandson, in time he will come to accept him as your new partner, especially if you are on good terms with his parents.
Maybe afternoon tea at his house or in the park might be a good place to introduce him on the first occasion ? if that was your question, but don’t rush him, you are in the throws of a new marriage, but don’t expect him to love your new husband as you do, yet.