My dad is a big extrovert - he's a doctor - but he always loved [William] Shakespeare and he took us to tons of theater.

I remember somebody saying something to me about Frost/Nixon, when Anthony Hopkins does his famous speech, and the difference in the way Anthony did it was to dramatize, essentially, what was a documentary-style version of that speech. I remember someone saying to me, "There is artistic liberty."

I watched tons of archive footage of princess Margaret and listened to the music she loved; that was really immersive and brilliant.

I watched her do speeches, but the only footage we could find of [princess] Margaret was archive footage, which was of her public presentation of herself.

Marking the differences between them was really important. It just became second nature. When we were choosing pajamas or something, instantly you'd be able to spot: those are [princess] Margaret, those are [princess] Elizabeth. It became this sort of language, really, of the two sisters.

I did a lot before [being cast] because I knew how important it would be for playing somebody real, or attempting to - to show the team [the role] was something I would be fascinated to do. I read a couple of biographies and I watched everything I could find [about princess Margaret].

Everybody has an image of [princess Margaret], to a certain extent. But I felt it would have been harder if we were playing them as they are now. In a way, I don't know how much of a living memory we as a collective have of them in the '50s, when Margaret was 21 and this sort of Elizabeth Taylor. You don't think of your grandparents as being teenagers. You just can't - your brain just can't go there!