Joffrey Velaryon
Rhaenyra's third son by Laenor — named, with spectacular tactlessness, for the Knight of Kisses. Bonded young to the she-dragon Tyraxes.
The fuller tale
Rhaenyra's third son by Laenor carries a name chosen, with a tactlessness that says something about the queen's household humor, for the very Knight of Kisses whose relationship with his father was an open secret at court — Ser Joffrey Lonmouth, honored rather than concealed. The younger Joffrey bonds young to the she-dragon Tyraxes, the last of the black princes to claim a mount before the war overtakes the family's remaining childhoods entirely.
Too young for most of the war's major campaigns, he nonetheless finds himself, in its final and most chaotic days, in exactly the kind of situation the family has spent two seasons of fighting trying to keep its youngest members away from.
The page and the screen
Joffrey Velaryon appears only glancingly in the show's currently aired seasons, his eventual role belonging to episodes not yet broadcast; Fire & Blood, by contrast, carries him through to a specific and detailed final scene during the fall of King's Landing.
Where they stand, season by season
Their fate — if death has found them, it is written here. Open at your peril.
The books: Fell from Syrax over the burning Dragonpit (F&B, ch. 6)
When the mob stormed the Dragonpit, Rhaenyra's youngest tried to fly his mother's Syrax to save the dragons chained inside. Syrax threw him; the boy fell to the streets, and the Shepherd's faithful finished what the fall began.
The series has not yet reached this stage of the story; Joffrey's fate remains ahead of the current seasons.
Fire & Blood has him, in the chaos of the mob's assault on the Dragonpit, attempt to fly his mother's own dragon Syrax to save the chained and vulnerable dragons trapped inside the burning structure — a rescue attempt made by a boy with no bond to that particular dragon. Syrax throws him rather than answer to an unfamiliar rider, and Joffrey falls into the streets below, where the Shepherd's rioting faithful finish what the fall began.