Warning: spoilers for Game of Thrones ahead.
The Targaryen dynasty fulfilled its motto of "Fire and Blood" in the Game of Thrones series finale. After laying waste to King's Landing with her army and her dragon fire, Daenerys finally reached the Iron Throne, only to be killed by her lover (and surprise nephew), Jon, aka Aegon Targaryen, who has finally grown too horrified at her violence to let her continue on. After Dany dies, her last remaining dragon, Drogon, appears, and he spots Dany's body with Jon right by her. Drogon roars and rages - but he doesn't kill Jon.
It's unclear as to why Drogon doesn't kill Jon where he stands. After all, Jon just killed Drogon's mother, and dragons are not known for being the forgiving kind. One possibility is that Drogon outright cannot kill Jon, at least not with dragon fire. We've seen before that Targaryens - or at least some Targaryens - cannot be burned by fire, as Dany herself proved when she walked through a funeral pyre and emerged unscathed and with three hatched dragons. Drogon may have not bothered burning Jon because it would have no effect, although we've never learned whether or not Jon's Targaryen blood would protect him from fire, seeing as there's never been an opportunity to test that theory.
Another possibility is that Drogon doesn't want to kill the last dragon rider and the last Targaryen, so he turns his fury instead on the object that represents Dany's downfall: the Iron Throne itself. The fire rising in his throat that first seems like it's headed for Jon is instead turned on the throne of swords, heating it so intensely that the metal bends and melts, destroying the throne that so many have fought and died for. Drogon isn't seen again after taking Dany's body away, but his decision to spare Jon shows that he has more than just blind loyalty to his mother after all.