DDad died 23 yrs ago and DM has been with her "new" partner for 15 years. My DC are 8 and 5, and he's the only other grandad they've ever known. DM lives 200 miles away, so we don't see her and her partner that often, but the dc love him like a grandad, particularly DD who adores him.
For a number of very good reasons they are splitting up (this is a whole other story). It is likely, because of the distance, that we won't see him again. What don't tell the dc when they ask after him, want to ring him, notice he's not there at half term?