I don't have any other advice, but I'm so sorry for your loss of Charlie. I know it has to be hard on the entire family.
When my parents had two bullmastiffs, the female passed away in her sleep overnight from bloat. Ugh, I get sick just thinking of it. Both the male (who eventually became my dog) and female slept together in my parent's giant master bathroom, so he was with her when she passed, and he never looked for her. I suppose there must be some truth to animals understanding death.