Harry Potter star Daniel Radcliffe is not a fan of the sixth film in the boy wizard movie franchise, because he thought he was terrible.

The actor claims The Order of the Phoenix, the fifth film in the series, was his best work as Potter, but he stumbled as J.K. Rowling's literary hero in the follow-up, The Half-Blood Prince.

"In every movie up to the sixth one, you can see a big step forward in my acting," he tells Playboy. "And then it stopped, or went backward maybe, in the sixth film."

Radcliffe admits he raised his game in the fifth film as he worked on scenes with fellow Brits Gary Oldman and David Thewlis, but he hates watching scenes from The Half-Blood Prince.

He adds, "You're watching a mistake you made for 11 months."

"I had the idea that Harry was like a soldier traumatised by war, and as a result of that, he shuts down emotionally," the young star explains of his thinking ahead of the shoot. "That's not a bad idea, but it's not the most interesting thing to watch for two and a half hours."