Offer to babysit your new step-great-grandchild, OP. You'll make the mother happy, and it'll be a necessary reminder as to why you shouldn't pressure your son into having kids if he doesn't want them.

Gasp! How DARE your son not feel obligated to give you grandchildren! *eyeroll*

I know this kind of off topic but how old is the daughter that she is pregnant she has to be kind of young.

OK, because I'm getting confused reading all the comments who are calling OP the grandfather, the family relationship is: • OP • OP's son (who has no biological kids) • OP's son's girlfriend (who is close to her daughter) • Girlfriend's daughter (who is pregnant) So, if the son marries the girlfriend, *then* OP is step-grandfather to the girlfriend's daughter, and the baby will be the great-grandchild. OP, if being a grandfather means that much to you, be an active part of your son's life. That way, when the baby comes, your chances of being regarded as 'grandpa' (or yes, 'great-grandpa') will be higher.

if he's a dad to that woman's daughter, you're her grandpa. And you'll be a great grandpa

You get to be a great grandfather though. I just became a grandpa myself (Nov 1st) to my stepson & his wife's child my wife is 41, I'm 44, the son is 24 & his wife 20....just hope that the pregnant girl isn't carrying your biological grand kid..that could be really awkward to explain.

If they get married, you will be the pregnant daughter's grandfather (through marriage). You would also be a great-grandfather.

thts literally impossible...u r a grandfather because ur sons girlfriend has a daughter

Duuuude, that is tough

What? THEIR daughter can't call you Grandpa? *Family is what you make it, old man.