Credit: Jon Furniss/

Harry Potter's Daniel Radcliffe recently opened up to GQ UK about his secret addiction to alcohol, but Emma Watson wasn't really aware of her costar's struggles.

"To be honest, it's really not something that I genuinely know much about," she told David Letterman on the Late Show Monday night. "But as far as I know, he never took a sick day. He was like the most professional, amazing guy ever."

The actress admitted she and Radcliffe, 21, have a very different relationship when it comes to their consumption of "controlled substances."

"I mean, yes, I have tried spirits! Of course, I've tried spirits," she said. "We drink at 18 in the UK -- but I'm actually legal to drink now in the US. It's worth mentioning -- I'm 21!"

Watson also confessed to getting "very, very drunk once in my life, as everyone has."

"I have been drunk, and I'll bow to that!" she exclaimed, standing up and good-naturedly bowing to the crowd.