Book for 4 year. Losing a family dog to cancer.

Hi, I have a 4 year old boy that enjoys his books.

The family dog has been around since his birth, and he's bonded with her. But the dog has 2 months to live according to the vet.

I think reading a children's book about loss, or saying goodbye, might help us with coping skills.

Can anyone recommend a book for a 4 or old boy?