Son very anxious

It my be a time to explain to him about mortality in a way he can understand.

The most common way is to use a character on TV that he knows well who has died and explain that this happens to everyone  but it is OK and it is normal.

There is a good article about this here:

https://health.clevelandclinic.org/how-to-explain-death-to-a-child/

Now while this may be shocking for him you can now use the good news that grandad is still alive even though he is ill and there may be good times still ahead.

While the uncertainty will not sit well with him, it is worth getting him used to some of the uncertainties that are inescapable. Normalising death is a good way to take the sting out of the tail I found.

That would be my thoughts, but you know him best.

Thank you 

Thank you