The "new dragon" in the context of the popular series "House of the Dragon" refers to new dragon riders and their dragons introduced mainly in the second season. Three notable new dragon riders are Addam of Hull, Hugh Hammer, and Ulf the White, who are common folk with traces of Targaryen blood. They ride the dragons Seasmoke, Vermithor, and Silverwing, respectively. Addam of Hull claims the restless dragon Seasmoke, which was previously riderless after the disappearance of its former rider Ser Laenor Velaryon. Hugh Hammer tames Vermithor, an older bronze dragon once ridden by King Jaeherys I. These new riders emerge amid the ongoing conflict depicted in the show, bringing new dynamics to the dragon lore of Westeros.
If the "new dragon" question refers to a different context, such as a recent news event or another series or game, please specify. But in the current popular cultural context, the new dragons of note are these in "House of the Dragon" season 2.
