Is it common to realize how much a relative means to you only when they're on their deathbed?

I have never been overly close to my grandfather,I'm extremely close to my grandmother. I treated him with respect,and I do love him,but my emotional ties have always been,I thought,with my grandma. Now both of them are terminally ill,but my grandpa is in icu,on a respirator,and I find myself grieving him already. Is it common to realize you were closer than you thought to relatives you didn't feel close to when they were in good health?Why am I so grieved now,if I didn't feel a close emotional bond to him when he was healthy?