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

It was always said you couldn't have two sisters less alike. In a way [princess] Elizabeth was always internalizing everything and [princess] Margaret was always externalizing everything, so that became the basis. The storyline becomes about these two sisters: they're fighting for their position or trying to establish their identity in the world alongside each other and in relation to this establishment which only those two were a part of.

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."

It's this amazing combination to play, really, of somebody who's actually very fragile and hasn't really grown up properly yet - at least in a healthy environment - and has suffered immense loss with her dad - like that line where she says, [in the words of her father [King George VI], "Yes, 'Elizabeth is my pride but Margaret's my joy." She holds onto it!

[Princess Margaret] was always trying to radicalize things.

That external struggle mirrors the struggle of this life force of energy that [princess Margaret] was.