How very sad. As others have said, I knew about this potentially happening in humans with bee allergies,so it seems reasonable that it could happen to a dog.

Unfortunately, he couldn't just say "I just got stung by a bee, and now I don't feel good" like a person could and so you couldn't know. And, as bees are wild creatures, it would be nearly impossible to keep him away from them anyway. How terribly sad, I hope you have better luck with your next pup.