He was on Waltham's after coming from the vet's, but quickly went off of that. Was back to Rollover (his normal diet) because we couldn't get him to eat anything else. Then the vet suggested the rice and hamburger diet...which he loved for the past few weeks.
Thank you for your suggestions, however I'm afraid that this is the end of the road for him. We're putting him down tomorrow.
Again, thank you.