The film made just £40,000 after it was released in 38 cinemas across North America, following harsh reviews by critics, The Daily Mail reports.
Watts was considered a possible Best Actress contender for her portrayal of the late Princess in 'Diana', but reviews from the British press soon tossed cold water on those assumptions.
"'Diana' can only be described as a fabulously awful film," Mirror critic David Edwards wrote in his one-star review, which also calls the Oliver Hirschbiegel feature "lazy, mid-afternoon stuff."
Written by Stephen Jeffreys and based on the book 'Diana - Her Last Love' by Kate Snell, 'Diana' focuses on the princess' love affair with heart surgeon Hasnat Khan (played by former 'Lost' star Naveen Andrews).
"Poor Princess Diana. I hesitate to use the term 'car crash cinema.' But the awful truth is that, 16 years after that terrible day in 1997, she has died another awful death," wrote Guardian critic Peter Bradshaw. "This is due to an excruciatingly well-intentioned, reverential and sentimental biopic about her troubled final years, laced with bizarre cardboard dialogue - a tabloid fantasy of how famous and important people speak in private."
Watts has gone on record to discuss how conflicted she was about playing Princess Diana in the film. "The filmmakers came to me and it's a good script and it's very scary and I kind of wanted to say no but I couldn't," Watts said last year.
Do you think the film should have been made?