Why did Olenna poison Joffrey?

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Tags

1. #given
2. #joffrey
3. #tyrion
4. #poisoned
5. #stark
6. #dontos
7. #stone
8. #arranged
9. #reality
10. #olenna
11. #which
12. #hidden
13. #necklace
14. #poison
15. #process
16. #littlefinger
17. #worked
18. #hollard
19. #attached
20. #deliver
21. #sansa