why did ser criston kill joffrey?

best answer
  • The reason for him to literally murder Ser Joffrey to death was Rhaenyra. Ser Joffrey was getting married to Rhaenyra. Ser Criston also liked Rhaenyra but when he expressed his feelings to her she turned him down by saying that she couldn’t lose her crown and she had better duties to perform other than being involved in some love game.