Why did daenerys brother die?

Related questions

1. Is Jon Snow immune to Dragon Fire?
2. What made Khal Drogo sick?
3. Is Khal Drogo evil?
4. Will Jon Snow be resurrected in the books?
5. How does Drogo die in got?
6. Who kills Khal Drogo?
7. How old was Daenerys when she married Khal?
8. Which episode does Khal Drogo die?

Tags

1. #immune
2. #books
3. #viserys
4. #drogo
5. #targaryens
6. #immunity
7. #crown
8. #after
9. #demanding
10. #skull
11. #secondly
12. #emphasized
13. #implied
14. #rather
15. #poured
16. #molten
17. #tolerance
18. #first