The U.K. has denied Chinese dissident artist Ai Weiwei a six-month visa, saying that he failed to mention past criminal investigations on his application. “It is a matter of public record that you have previously received a criminal conviction in China, and you have not declared this," a letter stated. Ai was detained by Chinese authorities for 81 months in 2011, but never convicted of—or even charged with—a crime. He was instead granted a 20-day visa for his upcoming London show, whose installation he now won’t be able to supervise. Ai was given a passport by China this week after it was revoked several years ago.