SAN DIEGO (AP) — The question of whom the next Doctor Who will be is still a mystery.

Steven Moffat, who writes the landmark science-fiction story about a traveling time lord, says no one has yet been tapped to replace Matt Smith, who is exiting the role this year.

"We haven't done that yet," he said Sunday when asked at a panel on the show in the cavernous Hall H before a crowd bearing hundreds of sonic screwdrivers and who cheered wildly a trailer for the 50th anniversary show to be aired later this year.

Though fans did not get an answer, they were mollified by the scenes from the trailer that featured Smith with his predecessor, David Tennant, along with Billie Piper as Rose and actor John Hurt, too.