Yes, he has a step grandmother, but I imagine it’s a different type of relationship than the one he would have had with Diana, although I’m sure Camilla is great with all her grandchildren, step or otherwise.
I used to love Tracey Ullman's impersonations of Carole Middleton child minding George when he was a toddler. She would curtsey to him all the time whereas 'Camilla' would buy the most inappropriate toys and send him out to play with the dogs!