Bestselling author Dan Brown, who was to have been one of the headliners at BookCon, has canceled his appearance at the show. He was forced to bow out due to a family emergency.

“Unfortunately, Dan’s mother underwent brain surgery and is gravely ill,” Suzanne Herz, executive v-p and director of publishing at Knopf Doubleday, said in a statement. “He was very sorry to disappoint his fans but his family needs to be together at this time.”

Brown’s fans have had to wait four years for a new book from the bestselling author. Origin is due out from Doubleday in October. To date, his publisher has only released a single sentence about the book: “Origin thrusts Harvard symbologist Robert Langdon into the dangerous intersection of humankind’s two most enduring questions, and the earthshaking discovery that will answer them.”