How did Ser Joffrey Lonmouth really die?
To celebrate the marriage of Laenor Velaryon and Rhaenyra Targaryen, the king hosts seven days of tournaments and festivities.
Rejecting Rhaenyra's favor, Cristion Cole competes for Alicent Hightower. Also fighting for Leanor Velaryon is her boyfriend Ser Joffrey Lonmouth (a Knight).
Criston Cole beats Joffrey's helmet to pieces with Ser Criston Cole's favorite weapon, the Morningstar.
It makes Joffrey faint. And he remains unconscious for 6 days. He dies unconscious.
In House Of Dragon, this incident is different.