The 28-year-old actress reprises her role as the daughter of Willis' iconic character John McClane in the fifth instalment of the franchise, 'A Good Day to Die Hard' - due out next year - and revealed it was daunting to act opposite the A-list star.
She told Getty: ''It's amazing just to be part of the legacy because that John McClane is so iconic that being his daughter is an amazing feeling.
''I do get starstruck working with Bruce because even though he is such a nice guy he's a real movie star. I grew up watching his movies it is just really hard to get used to just being around Bruce Willis. I mean, he's Bruce Willis!''
In the film, John goes to Russia to help his wayward son John McClane Jr. (Jai Courtney) battle underground criminals.
Mary first appeared as John's daughter, Lucy, in 2007's 'Live Free or Die Hard'.
Since the first 'Die Hard' film was released in 1988, the franchise has earned more than $1 billion at the box office worldwide.
'A Good Day to Die Hard' is released in February.