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Author George R.R. Martin appears at Comic-Con to discuss the prequel, premiering on HBO next month, to the wildly successful “Game of Thrones.” Photo credit: R. Tapia for @Comic_Con via Twitter

The upcoming prequel to HBO’s “Game of Thrones” will explore the origins of the Targaryen dynasty, the cast and creators told fans at San Diego Comic-Con on Saturday.

House of the Dragon,” which debuts Aug. 21, takes place 200 years before the events of “Game of Thrones,” a medieval fantasy series that became a global phenomenon during the eight-season run that ended in 2019.

The new 10-episode series tells the story of a “generational war” among the Targaryens, executive producer Ryan Condal said.

“It begins at the absolute pinnacle of the dynasty, the height of their power, wealth and influence. They have the most dragons they will ever have,” Condal said. “It’s just before the bloom starts to come off the rose.”

Paddy Considine plays King Viserys Targaryen, who the actor described as “a man of good temperament, and a kind man, trying to keep the peace time going within the kingdom.”

“Doctor Who” star Matt Smith plays Prince Daemon Targaryen, the king’s younger brother. The pair have “quite a complicated relationship,” Smith said. Emma D’Arcy portrays Princess Rhaenyra Targaryen, her father’s chosen successor.

Also in the family tree is Princess Rhaenys Velaryon (Eve Best), who was passed over for the throne.

“She should have been the queen,” Best said of the character. “It’s kind of annoying that she isn’t. It’s also kind of annoying that people keep reminding her that she isn’t.”

The new series is based on author George R.R. Martin’s book “Fire & Blood.” Martin, who had issues with parts of “Game of Thrones,” said he had seen nine of the “House of the Dragon” episodes and found them “pretty amazing.”

“These books, these characters, are like my kids,” he said. “When you give your kids to people for adoption, you wonder how they will they be treated, will you recognize them?”

So far, “I’m really very happy,” he said.

Comic-Con concludes Sunday.

(Reporting by Lisa Richwine)