Daniel Radcliffe made his girlfriend Erin Darke's life a misery by constantly practising the accordion to prepare for Weird: The Al Yankovic Story.

The Harry Potter actor admitted to USA Today that the most difficult part of playing parody singer 'Weird Al' Yankovic in the upcoming biopic was learning how to play the accordion while singing and moving around a stage simultaneously.

To try to perfect his performance, Daniel put in many hours practising the instrument, much to the actress' despair.

"Making the film, I was practicing accordion every day in this small room in Los Angeles, and I think that was a lot for my girlfriend," he admitted. "There was no place for me to go, so Erin was hearing quite a lot. The first month of me learning the accordion, her life must have been misery. She was living in a world of hearing the opening bars of My Bologna, but never getting past that. Those weeks were rough. Now that we are back in New York, I can go in my own room and practise."

The British actor also grew a moustache to play the character so he only needed to wear a wig on set. He ended up "loving" his new facial hair and Erin took a liking to it as well.

"She liked the moustache more than she thought she would. By the end of the month, she was like, 'Don't keep it, but I don't hate it, either,'" he shared.

Weird: The Al Yankovic Story, also starring Evan Rachel Wood, Rainn Wilson, and Julianne Nicholson, is due to be released this autumn.

Daniel and Erin began dating in 2012 after meeting on the set of the movie Kill Your Darlings.