how did a third dragon be introduced in the sea battle in episode 1 of house of the dragon season 3

The “third dragon” in the Battle of the Gullet is introduced as a chaotic surprise, not a formal new rider reveal: Rhaena and Sheepstealer arrive mid- fight, and the wild dragon begins attacking indiscriminately, which throws the whole sea battle into confusion.

What happened

• The battle is already underway between Team Black’s naval forces and the Triarchy’s fleet when Sheepstealer appears.

• Rhaena’s arrival adds a new aerial threat, but because Sheepstealer is wild and not fully controlled, the dragon attacks friend and foe alike.

• That sudden disruption is what creates the “third dragon” moment viewers are talking about.

Why it matters

• Jacaerys notices the third dragon and tries to avoid striking Rhaena, which costs him precious seconds.

• That split-second decision leaves him exposed, and he is killed shortly after in the chaos of the battle.

• So the dragon’s introduction is narratively important because it directly changes the outcome of the fight.

In plain terms

It is basically a battlefield surprise entrance: Sheepstealer shows up, looks like an ally at first, then becomes a wildcard that reshapes the entire sea battle.

TL;DR: the “third dragon” was Sheepstealer, brought into the battle by Rhaena, and the big twist is that the dragon is untamed enough to make the fight even more dangerous.