The 44-year-old actress said that she was concerned about taking on the iconic role as she feared Britain's Prince William and Prince Harry might have problems with her portraying their late mother, reported Showbizspy.
"I was afraid of the comparison that comes with playing any iconic figure and because of her memory, we are fond of her memory," Watts said.
Princess Diana died in a Paris car crash in August 1997.
"And the way she died ... Is it going to open it all up again? We're certainly not trying to upset the boys, though they're men now. I hope they're okay with it," she added.