The actress, who plays the title role in Oliver Hirschbiegel's upcoming biopic Diana, admitted as she has previously that she is dreading the British public's reaction to her performance.
"I am dreading the reaction amongst the pubic to my playing her," Watts told The Sun. "You know that people will complain that you don't look enough like her, that you're not tall enough, all those things.
"It's very difficult to play someone who had such a deep impact and left such a lasting memory on the public."
Watts went on to say that she felt a responsibility to honour people's memory of Diana, which is still "very fresh".
"It's also more complicated and sensitive when you take into account her two boys - William and Harry," she mused. "But I want to do her justice and help tell her story truthfully."
Diana will focus on the last two years of the princess's life, including her relationship with Dr. Hasnat Khan, played by Lost star Naveen Andrews.
The actress has previously admitted that she initially wanted to turn down the role because it intimidated her, but couldn't bring herself to pass up the opportunity.
Diana is set for release in early 2013.
Diana picture gallery:
Copyright: Rex Features SIPA