Author Rick Riordan surprised fans of his Percy Jackson and the Olympians book series at New York Comic Con on Sunday, introducing a clip from the upcoming Disney+ show based on his children’s fantasy novels, Deadline reports.

Riordan appeared with his wife, Becky Riordan, at a panel at the Javits Center. “Let’s go to Camp Half-Blood and play capture the flag,” he said, before a five-minute clip from the series played.

Riordan’s series, about a boy who discovers he’s a demigod and helps defend the world from the evil Titans, launched in 2005 with The Lightning Thief. Five more books followed; the most recent, The Chalice of the Gods, was published last month. A seventh book, Wrath of the Triple Goddess, is scheduled for publication next year.

The books were massive bestsellers and spawned two film adaptations that Riordan has heavily criticized.

The Disney+ adaptation stars Walker Scobell as the title character, with Leah Sava Jeffries and Aryan Simhadri playing his friends. Other cast members include Jason Mantzoukas and Megan Mullally; actors Lin-Manuel Miranda, Timothy Omundson, and the late Lance Reddick will make guest appearances.

At the Comic Con panel, Jonathan E. Steinberg, an executive producer on the show, praised Riordan for his involvement with the series, saying, “It would be extraordinarily difficult to try to do it justice, to do it right, without the person who dreamed it, and I think without the person who really did the work to sell it, and to find this audience and this fan base.”

Percy Jackson and the Olympians is set to premiere on Dec. 20.

Michael Schaub is a contributing writer.