Daniel Radcliffe has missed the first day at his first-ever Comic-Con!

The Harry Potter star got stuck in Toronto because of a visa hiccup that kept him from entering the States.

"He's stuck in Toronto with visa problems," the New York Post reported.

The British actor, who celebrated his 25th birthday this week, was north of the border for a premiere of his movie What If with actress Zoe Kazan. He was scheduled to arrive at the Comic-Con to promote his movie Horns.

Adapted from the book by Joe Hill, Horns stars Radcliffe as a character, who wakes up having grown horns after possibly killing his girlfriend.

Other projects being pumped at Comic-Con this week include HBO's Game of Thrones, Marvel's Avengers: Age of Ultron, Peter Jackson's The Hobbit: The Battle of the Five Armies and the long-awaited Mad Max: Fury Road with Tom Hardy.

According to Page Six, Radcliffe was in the process of upgrading his current P-2 visa, designated for foreign actors and entertainers, to an O-1 visa for "individuals who possess extraordinary ability in the sciences, arts, education, business or athletics."

Radcliffe had been approved to upgrade to the O-1, but he needed a "stamp from the US Embassy" in Toronto to travel back to the States and "their computer system was down," the source said.

Radcliffe ultimately did arrive in San Diego, later in the evening.

He was just in time for a scheduled Comic-Con panel later afternoon with his co-star Juno Temple and director Alexandre Aja.

Horns is being released by the Weinstein Company's Radius-TWC label.