Difficult grandad ignoring granddaughter - advice needed please?

Briefly as possible - I'm at a loss and need some help with this and who better to ask than some grans/granddads.
We were all shattered by my mum's sudden and unexpected death 4 years ago. My dad ( in his nineties and fit as a fiddle) has gradually recovered with lots of help and some medication for his anxiety and depression. He lives independently, drives, visits friends and is feisty and determined to keep going, but also lonely. The problem is that he has one grandchild (my daughter) who is 13 and since just after Mum died, he has ignored her! I'm an only child too! We visit every school holiday and stay with him and I phone every other day as we don't live nearby.

At first I put his behaviour down to depression as he was not himself at all. He stayed with us for long periods and I spent a lot of time visiting him so that he was not alone. He made some new friends and things improved a lot. But we have just come back from yet another visit, and he totally ignored his granddaughter again and I am in a rage! She is a lovely girl but has difficulty communicating and is very shy, so won't start a conversation and doesn't know what to say anyway! We have explained this (and he knows anyway as it's not new) but he ignores it and always brings the subject back to himself. He just looks straight past her and can sit at a table for a meal and not even look at her once. Yes I have tackled him about it and he gets very angry and defensive and refuses to talk.

I should mention that my mum was the loving gran and although he did take an interest it was mum who made a fuss and did everything. I am angry and upset and feel stuck - I either don't visit him (which I don't want to do, of course), or else condone his behaviour by carrying on as if everything is ok. No one else knows - his friends have no idea and we don't have a big family so it's just us. There is no logic to it and he blames his GD for not making an effort to speak to him! Unsurprisingly she doesn't want to go any more and neither do I or my husband to be honest! We even considered moving to be nearer to help him out but this situation is spoiling the whole relationship. He is very self-centred and tends to blame other people - it is impossible to have a calm discussion - I have tried but he refuses to discuss it and just says that he wishes that things were better. He can and does make a huge effort with friends and is charming and helpful to others which I find puzzling and very upsetting. Does anyone have any advice please?