Naomi Watts and Liev Schreiber.

High expectations ... Actress Naomi Watts, pictured with husband Liev Schreiber, initially turned down the role. Photo: AP

Naomi Watts says playing Princess Diana in a biopic about the late British royal's life has helped her understand her better.

The actress explained how being a mother-of-two in the public eye herself has meant she can relate to some extent with Diana's struggle to maintain a private life.

The 44-year-old star has learnt the impact that constant press intrusion had on the princess' life. "Most of the time I go completely under the radar but I do understand a little the pressure and how awful it must have been for her," Watts told Australian Vogue magazine.

Naomi Watts as Princess Diana in the film 'Caught in Flight'. Click for more photos

First look at Naomi Watts as Princess Di

Naomi Watts as Princess Diana in the film 'Caught in Flight'.

  • Naomi Watts as Princess Diana in the film 'Caught in Flight'.
  • Naomi Watts as Princess Di.
  • Naomi Watts as Princess Di.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • Naomi Watts as Princess Di.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • She's got the look … Naomi Watts as Diana, Princess of Wales.
  • Naomi Watts, left, is playing Diana, Princess of Wales, in an upcoming film.

"She was properly isolated because of the media attention and, as a result, paranoid. She didn't know who to trust and that is horrible. Such a lonely idea ... a horrible way to live."

Watts was reluctant to accept the role in the controversial movie, and initially turned it down. She feared she wouldn't be able to do the role justice but eventually agreed to take on the part due to her fascination with complex characters.

"In the case of Diana, of course, there is a huge pressure to look right, to have good hair, to walk and speak like her. And I instantly thought, 'Oh no, I'm going to fail at that because the comparisons are going to be monumental,"' Watts explained.

"I'm always interested in complicated women, in women who are full of contradictions: strength, vulnerability, success, loneliness and all those things. Diana exemplified that in major ways. She was a great mother, did a lot of things with AIDS charities and the landmines, and had an extraordinary life, but her life was filled with tragedy and, of course, ended in the most tragic way."

AAP/CM