Emma Watson's university commitments meant she had to have ''a lot of doubles'' while shooting 'Harry Potter and the Deathly Hallows Part 2'.
The British actress - who has played Hermione in all of the seven films based on the books by J.K. Rowling - was doing college work at Brown University in the US while shooting was ongoing, and Rupert Grint, who plays Ron Weasley, reveals special techniques had to be employed because she wasn't always available.
He said: "She wasn't here a lot, really. We had to shoot around her, really, because she had commitments for her university. She had a lot of doubles. They made a mask of Emma's face, a prosthetic for wide shots.
"She was there for big days and really important scenes and stuff. But I don't know how she did it, really. It'd be so weird to be in that school environment and then be on set. I couldn't do it."
In the final part of the last movie, the cast - including Daniel Radcliffe, who has played the titular boy wizard for 10 years - are aged to put themselves in their mid-30s, and Rupert admits it was strange watching himself "deteriorate" while getting made up.
He told the Los Angeles Times' Hero Complex Blog: "It was really quite terrifying, sitting in the makeup chair and gradually watching your face kind of deteriorate. Initially, we had to reshoot the end. I had a massive fat suit. We had to learn how to move like an older person. We had kids as well. I had this weird Donald Trump kind of hairstyle."