Penelope Cruz plays Javier Bardem's tempestuous ex-wife in Woody Allen's new comedy, 'Vicky Cristina Barecelona,' and she tells ET what makes her character tick!

"In many ways I didn't want to portray a crazy person; I wanted to get to really understand the reality that she lives in -- the one that she defends," the Oscar-nominated star tells ET's own Thea Andrews.

In theaters August 15, 'Vicky Cristina Barecelona' stars Scarlett Johansson as an emotionally and sexually adventurous American woman in Barcelona who becomes romantically entangled with a charismatic painter (Bardem) and his turbulent ex-wife (Cruz).

"I was always worried about doing too much, because [my character] is so big all the time and has so much energy," says Penelope. "She's a very damaged and unstable person emotionally and mentally."

She says that working with Woody was quite easy, however, and that while he has the whole movie mapped out in his mind, he was always open to her ideas about the character.

"I'm a huge fan of Woody Allen's work," says Penelope of the auteur, whom she calls "a master." "I was very excited when I found out about this opportunity."

Watch ET for more with Penelope!