Stuck up grandparents or what?

My friend and his girlfriend recently had a child out of wedlock, and both their parents' are delighted at the joy of their new granddaughter. However, the friend's grandparents will not acknowledge the child as their great-granddaughter since she was born out of wedlock. Understandably both my friend and his girlfriend are upset about this, especially when the grandparents were rather cruel and insensistive in giving their view on the matter. I mean, alright, the older people in our society have a different view on unmarried parents than the people of today, but to disown your own great-grandchild because of their parents marital status is just not on. How should my friends deal with this? I know if that were my grandparents, I would have told them exactly what I thought of them without mincing my words.